Argentina has been hailed the world leader in transgender rights after its citizens were given the right to change their legal and physical gender identity without humiliating testing.
The gender identity law won congressional approval with a 55-0 Senate vote on Wednesday night.
It allows citizens to undergo gender realignment surgery without having to pass judicial, psychiatric and medical tests beforehand.
The Argentinian government legalised gay marriage two years ago.
Activists and academics who have tracked gender identity laws and customs worldwide said that no other country has gone so far to embrace gender self-determination.
In the United States and Europe, transgender people must submit to physical and mental health exams and get past a series of other hurdles before getting sex-change treatments.
Argentina's law also is the first to give citizens the right to change their legal gender without first changing their bodies, said co-director of New York's Global Action for Trans Equality Justus Eisfeld .
"The fact that there are no medical requirements at all - no surgery, no hormone treatment and no diagnosis - is a real game changer and completely unique in the world," said Mr Eisfeld, who researched the laws of 47 countries for the Council of Europe's human rights commission.
Marcela Romero, who was born a man but got a sex-change operation 25 years ago, spent 10 years arguing in Argentina's courts before a judge ordered the civil registry to give her a new identity card listing her gender as female.
"It's something humiliating - many of us have had to endure psychiatric and physical tests," she said. "With this law we'll no longer have to go through this."
Most Argentinians identify as Catholic, and the church opposes the law.
Director of the church-sponsored Centre for Bioethics, Personhood and Family Nicolas Lafferriere said: "Argentinian MPs are introducing profound changes in society that don't respond to any social demand and without taking into account the real consequences.
"We have found ourselves faced with the most permissive law in the world in this area."
If you appreciated this article then please consider donating to the Morning Star's Fighting Fund to ensure we can keep developing your paper.
Official inflation figures understate the real extent of rising costs, but even the government's own CPI scheme lays bare the ongoing misery for working people and those dependent on benefits.
The Con-Dems have had it their way too long. We have to turn this country around
How high-quality primary schooling could help solve global poverty