According to the Portuguese RTP news agency, the law was approved in a 136-78 vote with 4 abstentions.
Portugal's President Marcelo Rebelo de Sousa will need to make the final decision concerning the adoption of legislation.
The law establishes that adults over the age of 18 who suffer from an incurable disease will be allowed to ask for medical assistance in dying.
Portugal will become the fourth country in Europe and the seventh in the world that officially allows euthanasia.