The Argentinian Senate, just days after an influential committee rejected the proposal, has voted to legalise same-sex marriages despite opposition by huge numbers of Argentinians.

The act makes Argentina the first Latin American country to legalise same-sex marriage.

The proposal was firmly backed by President Cristina Fernandez, and had been approved by Argentina’s lower house in May.

The Senate’s vote meant that same-sex marriage automatically became law this morning after it was approved by a senate majority. The law was adopted 33-27 following a 15-hour debate.

The law had been strongly opposed by the Roman Catholic Church and evangelical groups, which drew 60,000 people to a march on Congress on the eve of the pivotal vote. Last week, a petition with over 600,000 signatures opposing same-sex marriage was handed in to the Senate.

A recent nationwide poll suggested that a strong plurality of Argentinians, 46 per cent, were opposed to the proposed legislation, while only 40 per cent supported it. A large group, 14 per cent, had no opinion, according to the survey.

Supporters and opponents of the law held rival vigils through the night outside the Congress building in Buenos Aires.

Same-sex civil unions have been legalised in Uruguay, Buenos Aires and in some states in Mexico and Brazil. Mexico City has legalised same-sex marriage. Colombia’s Constitutional Court granted same-sex couples inheritance rights and allowed them to add their partners to health insurance plans.

However, Argentina has become the first country in Latin America to legalise same-sex marriage, which generally includes the right to adopt children.

The new law broadly declares that “marriage provides for the same requisites and effects independent of whether the contracting parties are of the same or different sex.”

President Fernandez’s husband, former president Nestor Kirchner, has also been a strong same-sex marriage supporter. Some opposition leaders have accused the couple of promoting the initiative to gain votes in next year’s presidential elections, when Mr Kirchner, who is currently a congressman, is expected to run again.

Supporters of traditional marriage also offered a civil union compromise. But gays and lesbians rejected this because it would not allow adoption or access to in-vitro fertilisation. The compromise would also have recognised the conscience rights of public servants.