A close vote is likely on Thursday and if it passes, the measure would go to the Senate. President Mauricio Macri says he opposes abortion, but would not veto the bill.
Argentina's legislature on Wednesday began debating a measure that would allow elective abortions in the first 14 weeks of gestation.
It's a debate that has sharply divided the homeland of Pope Francis.
Crowds of supporters and opponents of the measure have been watching the debate on large screens set up outside Congress.
Abortion-rights student demonstrators also occupied about a dozen public schools in the capital.
'Abortion needs to be legalised'
"I am here because we have the full right to decide over our bodies, abortion needs to be legalised," said Diana Silvero, a pro-legal abortion activist.
"Women and trans people will continue carrying out abortions, be it legal or not but by making it legal, what will change is that the young women in marginalised situations will stop dying (due to having unsafe or clandestine abortions) because the rich can pay for (safe) abortions."
Activists in favour of legalised abortion claim about a third of maternal deaths in the South American country are related to clandestine abortions.
A close vote is likely on Thursday. If it passes, the measure would go to the Senate.
President Mauricio Macri says he opposes abortion, but would not veto the bill.
Change in constitution sought
"This is not about dogmatic, philosophical or religious questions, our legal system in Argentina and the international pacts to which we adhere to guarantee life from the moment of conception," said Jose Cano, National Deputy for Radical party.
"For the congress to move forward in sanctioning a reform of this nature, first we need to change the constitution."
Argentina allows abortion only in cases of rape or risks to a woman's health.
Rights groups have criticised a requirement for a judge's permission, which often results in lengthy delays or denial of the procedure.
Deeply Catholic tradition
Like most of Latin America, Argentina has a deeply Catholic tradition, which Catholic and Christian churches opposing the measure.
Latin America and the Caribbean have some of the world's most restrictive abortion laws, with six countries in the region operating blanket bans.
Argentina's neighbour Uruguay is an outlier in Latin America in permitting abortions.
A Chilean court last year upheld a law legalising abortion in certain cases. Chile had been one of only a handful of countries worldwide where the procedure was banned without exception.
If Argentina legalises abortion, it would be the largest country in Latin America to do so.