If you are a Portuguese citizen living in Portugal:
The registration in the electoral list is automatic, based on the citizen's card information, for all Portuguese citizens living in Portugal over the age of 17.
If you are a Portuguese citizen living abroad:
The registration in the electoral list is automatic based on the information on the citizen card, however, portuguese citizens residing abroad may, at any time, request the cancellation of their enrolment at their registration office or on the euEleitor portal a
The options of cancellation or registration in the electoral register is included in the procedure for obtaining, changing address or renewing the citizen card.
If you are a foreign citizen resident in Portugal:
Voter Registration is voluntary, with the exception of Brazilian citizens who have equal rights and duties and political rights, status, and are automatically registered in the parish corresponding to the address on the citizen card.
As voter registration is voluntary, the citizens themselves request it with the census commission / parish council of their area of residence, under the following terms:
If you are a citizen of another EU country with legal residence in Portugal:
You must identify yourself with a valid identification title and provide proof of legal residence in Portugal by through means that proves it, namely Union Citizen Registration Certificate or Union Citizen Permanent Residence Certificate.
If you are a citizen of a Portuguese-speaking country (Brazil and Cape Verde):
And you have been legally resident for more than 2 years, you must identify yourself and provide proof of residence with a valid residence permit.
If you are a citizen of another foreign country:
And you have been legally resident in Portugal for more than 3 years, you must identify yourself and provide proof of residence with your valid residence title.
(Note: Only nationals of countries that are recognised as citizens with active electoral capacity may be registered in the electoral register. See declaration no. 29/2021, of 25 March 2021)
Autenticação.GOV