Chile's parliament is set to approve a long-awaited bill Tuesday to legalize same-sex marriage, joining just a handful of countries in majority Catholic Latin America with similar laws.

It will also enable married same-sex couples to adopt children.

Chile, which legalized same-sex civil unions in 2015, has been waiting for this bill since 2017, when it was sent to Congress by socialist then-president Michelle Bachelet.

In a surprise move, her conservative successor, Sebastian Pinera, announced in June he would seek the bill's urgent passage through Congress.

It was given the go-ahead by the lower house, or Chamber of Deputies, earlier this month, and must now be approved by the upper house, or Senate, before finally being signed into law by Pinera.

Supporters of the bill gathered in capital Santiago with rainbow flags and posters reading "Equal marriage, now!" before departing for Valparaiso, the seat of Congress, to attend the voting session.

"There are lots of nerves and excitement," one of the group, Ramon Gomez, said alongside his partner of 21 years Gonzalo Velazquez.

Same-sex marriage is already legal in six Latin American and Caribbean countries: Costa Rica, Ecuador, Colombia, Brazil, Uruguay and Argentina, as well as in 14 of Mexico's 32 states.

- 'Love does not discriminate' -

"We want to insist that this bill should become law right now. There can no longer be excuses for continuing to drag out the discussion in Congress while hundreds of families wait anxiously," Isabel Amor of the Fundacion Iguales LGBT rights group said ahead of the vote.

"Love does not discriminate, but the law does," added Lorena Grez, who with other activists delivered 20,000 signatures in support of the bill.

"In Chile, we are not recognized as a family," but instead treated as "second-class" citizens, she said.

The Senate hearing on the bill, which has the backing of the majority of Chileans according to polls, will be preceded by a decision of a parliamentary constitutional commission -- a step that could see the vote delayed by hours, or perhaps to another day.

The project has been consistently opposed by the most conservative bloc of Chile's ruling right wing, but has nevertheless obtained a majority "yes" vote at every step of the process to date in an opposition-dominated congress.

Majority support

On Monday, the Movilh LGBT rights group released the results of a survey in which 82.8 percent of same-sex couples, among 1,878 people interviewed, said they planned to marry once it is legal.

The issue deeply divides the two candidates headed for a presidential run-off on December 19.

Gabriel Boric, 35, who represents a leftist alliance that includes the Communist Party, supported the bill and voted "yes" in his capacity as lawmaker.

But 55-year-old, far-right candidate Jose Antonio Kast, who won 28 percent of first-round votes compared to Boric's 26 percent, campaigned against it.

A global Ipsos survey in June found that 65 percent of Chileans were in favor of legalizing gay marriage -- higher than the global average of 53 percent.

Sixty-seven percent supported adoption by homosexual couples.