International marriage: which law can apply?

There is no single answer as to which law governs an international marriage: the applicable legislation depends on connecting factors such as the spouses' nationality, domicile, place of celebration and, in some cases, the couple's express choice, making it essential to assess the specific case and the jurisdictions involved.

Marriages between people of different nationalities, or celebrated in a country other than the one where the couple intends to live, may be subject to more than one legal system simultaneously — one for the marriage's formal validity, another for the property regime, and possibly a third for succession matters. Understanding this distinction avoids surprises at sensitive moments, such as divorce, succession or a change of country.

Formal validity — whether the marriage was celebrated in accordance with the required formalities — is generally assessed under the law of the place where the ceremony took place. But this is not an absolute, universal rule: each legal system may have its own exceptions and recognition requirements.

The couple's property regime typically involves different connecting factors, such as the spouses' common nationality, their first marital domicile, or the possibility of choosing the regime through a prenuptial agreement, where permitted by the jurisdiction. Binational couples are often surprised to discover that the regime presumed in one country is not automatically the one recognized in the other.

Civil capacity to marry — minimum age, impediments, consent requirements — is generally assessed under the personal law of each party, which can lead to situations where one spouse must documentarily prove their capacity under the law of their country of origin.

A marriage validly celebrated in one country is not automatically registered or does not automatically produce full effects in another. A registration, transcription or formal recognition procedure before the authorities of the other country is often required, especially when the couple wants the marriage to produce civil, property or immigration effects there.

• Assuming that the default property regime of the country of celebration will automatically apply where the couple comes to reside.
• Failing to register or transcribe the marriage in the country of nationality or residence of one of the spouses when required.
• Ignoring the need for a prenuptial agreement when a property regime different from the one presumed by law is desired.
• Treating a regime choice made without considering future changes of country of residence as final.
• Leaving the matter until divorce or succession, when the available options are already far more limited.

A marriage can be valid in two countries and still be subject to different property regimes in each of them.

1. 01Identify the nationality and domicile of each spouse at the time of marriage and after any subsequent change of country.
2. 02Check whether the marriage needs to be registered or transcribed in other countries relevant to the couple.
3. 03Assess the advisability of a prenuptial agreement, especially in binational marriages or those involving significant assets.
4. 04Confirm, before any change of country, how that change may affect the property regime already established.
5. 05Gather civil-status documentation duly legalized and, where applicable, translated.

Each of these points depends on the couple's specific jurisdictions — the country pages (/paises/brasil, /paises/portugal, /paises/paraguai) offer useful overviews, and /inteligencia-comparada allows regimes to be compared across countries. For couples already facing a concrete decision, the International Legal Diagnosis at /diagnostico is the recommended path for a personalized analysis.

International marriages do not follow a single, automatic legislation: the answer depends on which aspect of the marriage is at issue and which jurisdictions are connected to the couple. Planning these points in advance is what prevents complex disputes down the road.