Do new residents have to register at the mairie?

EU rules allow states to require Europeans to register with the local authorities, such as the mairie, if they wish to be considered permanent residents (non-Europeans must have residence permits). Consequently, article L121-2 of the law on immigration, Code de l’entrée et du séjour des étrangers et du droit d’asile, provides for Europeans to register within the first three months. However article L121-5 requires this to be put into action by a decree by the Conseil d’Etat, which was never done. It is therefore not required.

You may, however, wish to register as an elector for the local (mairie) and European elections, which is one of the rights of European residents in France. In many towns you can do this online; otherwise you apply to the mairie. Some allow postal applications. Find out more by putting in your postcode in the box at:
service-public.fr/particuliers/vosdroits/F1937

You will need an identity document eg. a passport, plus proof of residence, which is usually a utility bill dated in the last three months (if online, then scans, or if by post then photocopies). You also need to fill in form Cerfa n°12670*01 which can be obtained at: service-public.fr/particuliers/vosdroits/R16025

If you want to take part in the elections in a given year, you need to be on the lists by the end of the previous year; it is therefore advisable to apply by December 15 at the latest. However this will change by the end of 2019, when it will become possible until the sixth Friday before the election, or, if allowed by the mayor, 10 days before.