The Greek parliament passed a law on Tuesday to make it easier for people to change their legally recognized gender, a move that angered the Church but was welcomed as long-overdue by human rights groups.
The law will allow people to change their gender on official documents with a court ruling, and without requiring medical tests or sterilization, as is the case now.
It has been condemned as "immoral" by the Greek Orthodox Church and as a "monstrosity" by right-wing politicians.
Until now, anyone needing to officially change their gender had to be diagnosed with a "gender identity disorder" and have their reproductive organs removed, a practice condemned by human rights campaigners.
"Absolutely no tradition, no perception of family calls for people to be sidelined or tossed aside into a social and institutional abyss," Prime Minister Alexis Tsipras, who supported the law, told a heated discussion in parliament.
The law applies to anyone over the age of 15 and allows a person to change legal gender twice. Applicants must not be married and a final decision will be taken by a court.
The main opposition conservative New Democracy party voted against the bill saying it was a "sloppy" attempt to divert public attention from Greece's financial woes.
"Your only goal is to stay in power," said conservative lawmaker Simos Kedikoglou. "You've found various methods of deception and this bill is the latest proof."
Supporters rallied outside parliament during Monday's debate, holding a banner reading: "Transgender rights are human rights."
The Church had urged the government to withdraw the bill.
"For every human, gender is a sacred legacy. It is a precious thing for a woman to know about her feminine nature, and for a man to be aware of his male nature," Bishop Nicolaos of Mesogaia told Greek Skai TV.
The Church, he said, embraced "people with difficulties."
The bill passed by 171 votes in the 300-seat parliament, but it exposed fissures in the ruling coalition of Syriza and right-wing Independent Greeks party.
Most Independent Greeks approved the bill in principle but voted against an article setting the minimum age at 15, arguing that was too young.