The issue has divided the country pitching politics against faith.
Portuguese lawmakers will vote on Tuesday on proposals from four left-leaning parties to allow assisted suicide.
It comes after a petition in 2016 garnered enough signatures to force a parliamentary debate. Ana Figueiredo was one of those who signed after her cancer-suffering father shot himself in 2014. He left a letter explaining that he could no longer stand the pain.
"To shoot himself with a gunshot to his temple to stop his own pain - which he could no longer endure and he had no more hope although his life had been full of hope - I think it is not dignified for anyone."
Portugal has recently legalised abortion and same-sex marriage, but the assisted suicide arguments will once more pitch politicians against faith. It is a strongly Catholic country and even some of the socialist parties' own members say they will vote against the bill.
"These gentlemen (referring to lawmakers) want us to become health professional executioners of the death of those in pain," said Sara Sepulveda, an anti-euthanasia protester. "This is what's at stake and we do not want that."
The conservative Popular Party and the Communist Party say they will vote against the proposals .