Since 1 January 2021, British citizens living in France have been third-country nationals. A British passport no longer carries European Union citizenship, and every stay beyond a short visit depends on a visa or a residence permit. For Britons who have made France their home, French nationality is the only status that restores the full set of rights they lost with Brexit: the right to live, work and travel across the Union without asking permission, the right to vote in every French election, and unrestricted access to the French labour market. This guide explains, for a British reader, the two realistic routes to a French passport after Brexit — naturalisation by decree (naturalisation par décret) and acquisition by marriage (déclaration de nationalité à raison du mariage) — what the prefecture (préfecture, the State office that handles nationality files) examines, how British citizenship is preserved, and how to challenge a refusal, an adjournment (ajournement, a postponement of the application) or a government objection (opposition). Readers still at the residence-permit stage should first settle which long-stay visa and which carte de sjour a British newcomer needs after Brexit, then return here once settled.
French nationality law sits in the Civil Code (Code civil), and the conditions below are quoted from the provisions in force on 3 October 2026, each verified against Légifrance. Years spent in France under the Withdrawal Agreement residence permit (the WARP card) count as lawful, continuous residence like any other valid carte de séjour, so a Briton who settled before the end of the transition period starts from the same position as any other long-term foreign resident. What follows is structured around the two questions British clients ask most often: how do I qualify for naturalisation by decree, and how does marriage to a French citizen change the picture.
I. How does a British resident obtain French nationality by decree after Brexit?
Naturalisation by decree is a favour of the State, not a right that flows automatically from years of residence. The Civil Code states the principle in one sentence: “l’acquisition de la nationalité française par décision de l’autorité publique résulte d’une naturalisation accordée par décret à la demande de l’étranger.” Because the decree is discretionary, the administration may lawfully refuse an applicant who meets every formal condition yet whose naturalisation is not considered opportune — a point the courts repeat constantly, as shown below. The practical consequence is that a British file must do more than tick boxes: it must persuade.
A. What are the five-year residence, assimilation and good-character conditions for a British applicant?
The first hurdle is the qualifying period of residence, known as the stage. “la naturalisation ne peut être accordée qu’à l’étranger justifiant d’une résidence habituelle en France pendant les cinq années qui précèdent le dépôt de la demande.” Habitual residence means the centre of the applicant’s private and family life must be in France throughout those five years: paying French income tax as a resident, holding a valid residence permit without gaps, and being able to show continuous address history through tax notices (avis d’imposition), employment records and housing documents. Short holidays in the United Kingdom do not break the period, but a posting abroad or a year in which the applicant was mainly tax-resident elsewhere can reset the clock, and the prefecture checks the residence-permit history line by line. Two further residence points matter. The qualifying period can fall to two years for a foreigner who has completed two years of higher education leading to a French university diploma, who has rendered or can render important services to France, or who shows an exceptional integration record in civic, scientific, economic, cultural or sporting life, under article 21-18; and certain categories, including refugees and foreigners who have served in a French army unit, may be naturalised with no qualifying period at all under article 21-19. Separately, “Nul ne peut être naturalisé s’il n’a en France sa résidence au moment de la signature du décret de naturalisation.” A Briton who files after five years in Lyon and then moves back to London before the decree is signed will fail at the last step.
The second hurdle is assimilation to the French community (assimilation à la communauté française), tested at a personal interview at the prefecture. “Nul ne peut être naturalisé s’il ne justifie de son assimilation à la communauté française, notamment par une connaissance suffisante, selon sa condition, de la langue, de l’histoire, de la culture et de la société françaises, dont le niveau et les modalités d’évaluation sont fixés par décret en Conseil d’Etat, et des droits et devoirs conférés par la nationalité française ainsi que par l’adhésion aux principes et aux valeurs essentiels de la République.” In practice the interview covers spoken French, knowledge of the institutions and values of the Republic, and the applicant’s daily integration. The same article fixes the expected language level functionally: “L’intéressé justifie d’un niveau de langue lui permettant au moins de comprendre le contenu essentiel de sujets concrets ou abstraits dans un texte complexe, de communiquer avec spontanéité, de s’exprimer de façon claire et détaillée sur une grande variété de sujets.” A certificate from an approved language body helps, but it never replaces the interview itself, and the interviewing officer’s report carries decisive weight. Professional integration is treated as an essential component of assimilation: the official service-public guidance states that stable and sufficient income to support the applicant and the tax household is required, and prefectures routinely ask for employment contracts, payslips and tax notices covering several years. British retirees with a steady pension, British employees on permanent contracts and the self-employed with declared French income all satisfy this expectation; a long spell without declared work is the single most common ground for postponement, as the case law examined below confirms. At the end of the examination the applicant signs the charter of rights and duties of the French citizen (charte des droits et devoirs du citoyen français), which restates the principles, values and symbols of the Republic.
The third hurdle is good character (bonnes vie et mœurs) and the absence of disqualifying convictions. “Nul ne peut être naturalisé s’il n’est pas de bonnes vie et mœurs ou s’il a fait l’objet de l’une des condamnations visées à l’article 21-27 du présent code.” Article 21-27 then excludes anyone convicted of crimes or offences against the fundamental interests of the Nation or of terrorism, anyone sentenced to six months’ imprisonment or more without suspension for any offence, anyone subject to an expulsion order that has not been expressly lifted or to a French-territory ban (interdiction du territoire français) that has not been fully served, and anyone whose stay in France is irregular. Minor road-traffic matters long spent do not automatically block a file, but any recent custodial sentence, an unexecuted removal order or a period of unlawful stay is fatal to the application. British applicants should therefore regularise every administrative detail before filing: an unbroken chain of valid residence permits, a clean criminal-record extract, and tax returns filed every year of the qualifying period. Where a foreign conviction exists, it may in some cases be left out of account, but only through a decree issued after the formal opinion (avis conforme) of the Council of State (Conseil d’Etat, France’s supreme administrative court).
B. How is the file lodged, what do rejection and adjournment mean, and how do you challenge them?
The application is lodged online through the dedicated nationality portal (téléservice), with the applicant preparing the originals of every document for the interview that follows if the file is declared admissible. The official guidance warns that the examining service may demand additional documents or steps within a fixed time limit, and that a file is closed without examination (classement sans suite) if the deadline is missed — a trap for applicants who move house mid-procedure and stop receiving post. The interview at the prefecture verifies assimilation in person, and a reasoned decision follows: grant, rejection (rejet), declaration of inadmissibility (irrecevabilité) where a legal condition is missing, or adjournment. The governing decree of 30 December 1993 provides that “Si le ministre chargé des naturalisations estime qu’il n’y a pas lieu d’accorder la naturalisation ou la réintégration sollicitée, il prononce le rejet de la demande. Il peut également en prononcer l’ajournement en imposant un délai ou des conditions.” An adjournment is therefore not a refusal on the merits: it postpones the application, typically by two years, and once the period expires or the conditions are met the person may file again. Every such decision must be reasoned: “Toute décision déclarant irrecevable, ajournant ou rejetant une demande de naturalisation ou de réintégration dans la nationalité française prise en application du présent décret est motivée”, so that the applicant can usefully discuss its grounds. In Paris and the wider Île-de-France, files are lodged through the same national online portal, the interview takes place at the competent prefectural nationality service, and Parisian applicants should anticipate the same evidentiary demands with a capital-city gloss: leases and utility bills in a tight rental market are scrutinised for genuine continuous address history, cross-border commuters who kept a London employment base must show that France truly remained the centre of their life, and anyone who changed arrondissement mid-procedure must update the address on the file immediately to avoid a closure for missed correspondence.
Because naturalisation is discretionary, judicial review is limited but real. The courts repeat that “L’autorité administrative dispose, en matière de naturalisation ou de réintégration dans la nationalité française, d’un large pouvoir d’appréciation. Elle peut, dans l’exercice de ce pouvoir, prendre en considération notamment, pour apprécier l’intérêt que présenterait l’octroi de la nationalité française, l’insertion sociale et professionnelle de l’intéressé.” Those sentences come from a July 2026 judgment of the Nantes Administrative Court of Appeal concerning a German resident who had lived in France since 1989, raised two French children there, held French architecture and planning diplomas, yet had spent more than four years without paid employment before signing a three-year fixed-term contract and still being on probation when the minister postponed her application by two years: CAA Nantes, 22 July 2026, no. 25NT03094. The court held that “la décision ministérielle contestée du 6 mars 2023 n’est pas entachée d’une erreur manifeste d’appréciation” — the minister’s assessment was not manifestly wrong — and that neither the length of residence nor deep family roots in France affected the legality of a postponement grounded on incomplete professional integration. The lesson for British applicants is blunt: decades of residence and French-born children do not compensate for a weak employment record at the date of the decision, and an adjournment founded on a recent return to work will survive judicial review. The same judgment confirms, however, that the decision must identify the legal provisions and the facts relied on so the applicant can argue against them, and a postponement that merely recites a formula without concrete findings can be annulled for defective reasoning. A refusal or adjournment is challenged by an application for judicial review (recours pour excès de pouvoir) within two months of notification, usually preceded by an informal appeal to the minister (recours gracieux) that extends the time limit while it is examined. The judge verifies the accuracy of the facts, the sufficiency of the reasoning and the absence of a manifest error of assessment; the judge does not substitute a personal view of whether the applicant deserves to be French. New evidence arising after the decision — a permanent contract signed the following month, for example — belongs in a fresh application once the adjournment period expires, not in the court file.
II. How does the British spouse of a French citizen become French by marriage and keep both passports?
Marriage to a French citizen opens a declaratory route that is structurally more favourable than naturalisation by decree, because it rests on an entitlement once the statutory conditions are met rather than on pure administrative favour. It remains fully available to British spouses after Brexit: nationality by marriage was never a European Union right, so the United Kingdom’s departure changed nothing in its mechanism, and only the surrounding residence-permit position of the British spouse changed. The provision has direct practical importance in Paris, where Franco-British couples are numerous and where many British partners previously relied on EU movement rights and never regularised a long-term French status.
A. What are the four-year marriage, shared life and language conditions for a British spouse?
“L’étranger ou apatride qui contracte mariage avec un conjoint de nationalité française peut, après un délai de quatre ans à compter du mariage, acquérir la nationalité française par déclaration à condition qu’à la date de cette déclaration la communauté de vie tant affective que matérielle n’ait pas cessé entre les époux depuis le mariage et que le conjoint français ait conservé sa nationalité.” Three elements deserve close attention from British declarants. First, the clock: four years of marriage is the minimum, extended to five where the foreign spouse cannot show three years of uninterrupted lawful residence in France since the wedding or cannot prove that the French spouse was registered on the roll of French citizens living abroad (registre des Français établis hors de France) during the couple’s shared life overseas — a detail that catches Franco-British couples who married in London, lived there for years and only recently moved to France. Second, the shared married life (communauté de vie affective et matérielle): the couple must show that living together, emotionally and materially, never ceased between the wedding and the declaration, through joint tax assessments, children’s birth certificates, a shared lease or ownership, and consistent address evidence; the spouses are interviewed together, sign a sworn statement (attestation sur l’honneur) that their shared life never ceased, and any separation, even brief, must be disclosed and explained rather than concealed, because a later discovery destroys the declaration. Third, the marriage itself: a wedding celebrated abroad must have been transcribed beforehand onto the French civil-status registers, and the French spouse must still hold French nationality on the day of the declaration. The foreign spouse must also show sufficient knowledge of the French language, at a level and under assessment rules fixed by decree in the Council of State. Declarations on grounds of marriage are received by the administrative authority, which issues a receipt (récépissé) once the documents proving admissibility are supplied, under article 26 of the Civil Code: that receipt starts the two-year period during which the Government may object, examined next.
Documentary preparation decides these files. British spouses should assemble the marriage certificate (less than three months old, or the transcription of a British wedding), the French spouse’s proof of nationality, joint tax notices for every year since the wedding, proof of continuous lawful residence covering the relevant years, and language evidence, well before the anniversary that opens the declaration window. Couples who lived in the United Kingdom after marrying should additionally secure the French spouse’s consular registration covering the overseas years, since without it the waiting period stretches to five years. Where the couple married in France at the town hall (mairie), transcription is unnecessary; where they married in Gretna Green, Islington or anywhere else outside France, transcription is a precondition and its processing time must be built into the timetable. The declaration route demands lawful residence too: the disqualifications of article 21-27 apply here as they do to naturalisation, so an irregular stay or a custodial sentence of six months or more without suspension blocks the declaration regardless of the genuineness of the marriage.
B. Can the Government block the declaration, do you keep your British passport, and how do you fight back?
The Government may object (faire opposition) to the acquisition by decree in the Council of State within two years of the receipt. “Le Gouvernement peut s’opposer par décret en Conseil d’Etat, pour indignité ou défaut d’assimilation, autre que linguistique, à l’acquisition de la nationalité française par le conjoint étranger dans un délai de deux ans à compter de la date du récépissé prévu au deuxième alinéa de l’article 26”, and where the Government objects the person is deemed never to have acquired French nationality, though acts validly done between the declaration and the decree of opposition stand. Two features of this regime deserve emphasis. An effective state of polygamy and certain convictions for sexual offences against young minors are deemed by statute to constitute lack of assimilation, so no debate is possible there. Everything else turns on the evidence of unworthiness (indignité) or non-assimilation, and the Council of State reviews the objection for exact application of the law. Two recent rulings show where the boundary falls. In CE, 29 May 2026, no. 502717, the Prime Minister had objected to a Malagasy husband’s declaration on the ground that he could not be regarded as assimilated to the national community; the Council of State annulled the decree, holding that “Il ne ressort pas des éléments versés au dossier par le ministre de l’intérieur que M. A… adopte un comportement ou soutient des thèses manifestant un rejet des principes essentiels de la République ou se tient délibérément à l’écart de la communauté nationale”, so that the Prime Minister had made an inexact application of article 21-4. A bare assertion of non-assimilation, unsupported by conduct or views showing rejection of republican principles or deliberate withdrawal from national life, does not survive review. Conversely, in CE, 30 November 2021, no. 451191, the objection was upheld against a Mauritanian husband who had married a French citizen in Nanterre in 2008 and then married a second wife in Mauritania in 2014, living in a state of bigamy for several years and fathering a child of the second wife: the Council of State held that in considering him insufficiently assimilated, the Prime Minister had not misapplied article 21-4. For British spouses the message is reassuring and precise at once: an ordinary integrated couple has nothing to fear from the opposition procedure, while concealment of a second household or of serious criminal conduct will defeat the declaration. Note the procedural coda of the 2026 ruling: the annulment of the decree of opposition entails no enforcement measure in itself — “n’implique par elle-même aucune mesure d’exécution” — so claims for an injunction ordering the minister to grant nationality were rejected, and a successful litigant should frame the claim around annulment plus, where useful, a request that the State re-examine the file.
Becoming French does not mean ceasing to be British. The United Kingdom expressly permits holding two nationalities: “Dual citizenship (also known as dual nationality) is allowed in the UK. This means you can be a British citizen and also a citizen of other countries. You do not need to apply for dual citizenship. You can apply for foreign citizenship and keep your British citizenship,” in the words of the official GOV.UK dual-citizenship guidance. On the French side, neither the conditions for naturalisation by decree nor those for acquisition by marriage require the applicant to renounce British citizenship, and the decree or recorded declaration simply adds French nationality to the British one. The practical gains are considerable: full EU citizenship with the right to settle and work in any Member State, the vote in all French elections including parliamentary and presidential ballots, eligibility for posts reserved to French or EU nationals, and French consular protection worldwide. Minor children share in the benefit automatically where the statutory conditions are met: “L’enfant mineur dont l’un des deux parents acquiert la nationalité française, devient français de plein droit s’il a la même résidence habituelle que ce parent”, provided the child’s name appears in the decree or the declaration. British parents should therefore check that every eligible child is named in the application, since an omitted child does not benefit from this collective effect (effet collectif) and would need a separate declaration later. The newly French Briton may also ask for the francisation of surname or forename alongside the application, and should then renew identity documents, inform the employer and the health fund (caisse d’assurance maladie), and consider the knock-on effects on the British side — pensions, domicile and estate planning — with advice that covers both systems.
Remedies against an objection follow the general law of judicial review: an action for excess of power (recours pour excès de pouvoir) before the Council of State against the decree of opposition within two months, built on the file as it stood when the Government decided. The strongest lines of attack are factual inaccuracy (the conduct relied on is denied or misdated), mischaracterisation (conduct incompatible with married life but irrelevant to assimilation to the French community), and defective reasoning where the decree recites conclusions without evidence. Declarations refused at the registration stage follow a different path, before the judicial courts (juridictions judiciaires), since registration disputes concern civil status; identifying the right judge at the outset avoids months lost in the wrong forum. In every configuration, the two-year opposition window means a declarant should keep the evidence of shared life and lawful residence available well after the receipt is issued, and should notify the prefecture of any change of address until the window closes, so that no decisive letter goes astray.
Conclusion
For a Briton settled in France, naturalisation by decree rewards five years of genuine, documented, working French life, while marriage to a French citizen offers a declaratory route after four years of unbroken shared life — and both routes leave the British passport untouched, since London allows dual nationality and Paris demands no renunciation. The files that succeed are prepared backwards from the refusal grounds: continuous lawful residence proved year by year, stable professional integration at the date of the decision, tested spoken French and lived knowledge of republican values, a clean record, and, for spouses, transcription of the wedding and unbroken evidence of life together. The files that fail usually fail on one of these points, and the courts will not rewrite a discretionary assessment that is factually accurate and properly reasoned, as the 2026 Nantes adjournment judgment demonstrates — just as they will annul an objection that asserts non-assimilation without proof, as the Council of State did in May 2026. A British applicant facing a postponement should therefore use the waiting period to repair the identified weakness and reapply, while a spouse facing an objection should challenge factual errors promptly before the Council of State. Prepared methodically and defended firmly, French nationality closes the Brexit parenthesis: the former EU citizen becomes an EU citizen again, this time by choice.