The country’s 230-seat parliament voted on Thursday to approve five right-to-die bills, with margins between 28 and 41 votes.
MP Isabel Moreira said the aim of the bills were to let people “make intimate choices, without breaking the law”.
“It is a historic day. It is a big day for democracy,” said Left Bloc’s leader, Catarina Martins, soon after the proposals were approved.
The move has seen protests outside the parliament in Lisbon and condemnation from the Catholic church.
Hundreds of people had gathered in the capital to protest ahead of the vote which has now set the country on course to become one of only a few countries to decriminalise the procedure.
Just two years ago the parliament rejected a bill to legalise voluntary euthanasia for terminal patients.
Francisco Guimares, 21, who was protesting said: “”I think life is an inviolable asset, human life has an inviolable value, consecrated by our Portuguese constitution – thank God.
“We must care for life until it comes to its natural end.”
Currently euthanasia and assisted suicide are only allowed in Switzerland, Luxembourg, Belgium and the Netherlands.
The bill will now be debated by the parliament’s constitutional affairs committee and after it has been discussed and potentially modified, it will be subjected to a final vote.