Residency conditions
Documents required
Legalised union
Obtaining Belgian nationality through marriage

Residency conditions
In Belgium, a marriage can be performed if one of the future spouses:

• is a Belgian citizen at the time of the ceremony
• has been resident in Belgium for more than three months
• in cases where neither party is a resident, one or both partners have applied for a temporary certificate of residence for marriage purposes (more below).

Residence in Belgium for more than three months can be demonstrated by any means:

• air ticket
• receipt for rent
• evidence of administrative formalities completed with the authorities
• etc.

Despite the above, it should be noted that a Registrar cannot refuse to perform a marriage on the grounds that the foreigner is in the country illegally.

If neither party is Belgian, they can apply for temporary residency for the purpose of getting married in Belgium.  In this case, one or both partners should visit the town hall when they arrive and request a Certificate of Residence for Marriage Purposes (Certificat de Domicile pour mariage/Bewijs van Woonst voor Huwelijksdoeleinden).

Documents required
The documents required for the union vary commune by commune. Some may request certificates of nationality and /or certificates of celibacy. In all cases, original copies of your birth certificate, passport and residency papers will be required.  If applicable, a final divorce decree showing the date of the divorce will also be required.

Contact the General Registrar's Office (Service de l'Etat civil) in your commune to ascertain which paperwork is required.You can also request a marriage certificate to the commune of your marriage via IRISbox (FR/NL), the online service desk of the Brussels-Capital Region. Please be aware that this service is available in French and Dutch only.

Legalised union
The ceremony itself must take place in the municipality where one or both of the partners are registered.  A civil ceremony is required to validate the union for official purposes; those being married in a religious ceremony must therefore ensure they visit an office of the state via the local municipality (Officier de l'Etat Civil/Ambtenaar van de Burgerlijke Stand) in order to legalise the union.  Two witnesses are required for this civil union.

Obtaining Belgian nationality through marriage
When a foreigner marries a Belgian, the former does not automatically receive Belgian citizenship.  In order to obtain Belgian nationality, certain conditions must be met, depending on the foreigner's status in the country.

Each partner must meet one of the following conditions: 

• they must have lived together for a minimum of three years in Belgium if , at the time of application, the foreigner does not have an authorisation to stay in the country for more than three months or to settle here; or
• they must have lived together for a minimum of six months in Belgium. This condition applies if, at the time of the application, the foreigner has authorisation to remain for more than three months in Belgium or to settle here.

The spouse wishing to apply for Belgian nationality must make a declaration before the municipal Registrar for births, marriages and deaths.

Moreover, in cases where the couple's main place of residence is outside Belgium, a declaration must be made at the Belgian embassy or consulate.

Source: http://www.belgium.be/en/family/becoming_a_belgian_citizen_by_marriage/, http://www.dfa.ie/home/index.aspx?id=80869, http://www.brussels.irisnet.be/living-in-brussels/family-and-private-life/living-together/mariage?set_language=en