SANTIAGO, Dec 7 (Reuters) - Chile"s Congress passed a law to legalize same-sex marriage on Tuesday, in a milestone for the conservative South American nation after a decade-long legal battle and with the country delicately poised ahead of a crossroads election this month. "Today is a historic day, our country has approved same-sex marriage, one more step forward in terms of justice, in terms of equality, recognizing that love is love," Minister of Social Development Karla Rubilar said after the vote. Chile"s Senate and lower house of parliament both voted heavily in favor of the bill on Tuesday, which had previously been partially approved in November before the Senate sent it back to a committee to clarify ambiguities. Current President Sebastian Pinera, who will leave office in March, has backed the bill and is expected to sign it into law. The vote culminates a process that began in 2017, when the first bill was introduced, backed by then-President Michelle Bachelet. Chile is now poised to join over 20 countries globally with legal same-sex marriage, including Argentina, Brazil, Colombia, Costa Rica and Uruguay in Latin America. "It is hard to believe that today we are taking this step," said Rolando Jimenez from LGBT rights group Movilh, one of the major backers of the bill and which helped spearhead Chile"s push to legalize same sex marriage for more than a decade. Chile will elect a new president on Dec. 19, choosing between progressive Gabriel Boric and social conservative Jose Antonio Kast, a practicing Catholic. The two offer wildly different visions for the country"s future. While Kast disagrees with same-sex marriage, he had said he would have signed the bill into law anyway had it been passed by Congress during a potential presidency of his. Chile has long had a conservative reputation even compared with its deeply Catholic Latin American peers. Still, a strong majority of Chileans now support same-sex marriage and Chileans have shown signs of moving left on social and cultural issues in recent years. Civil unions have been permitted in Chile since 2015, which affords same-sex partners many but not all the benefits of married couples, like the right to adoption. The law, which will come into effect 90 days after it is published in the Official Gazette, was cheered by rights groups and couples, opening the door for both parents in a same sex couple to receive full legal recognition. read more "This is cause for all Chilean society to celebrate," said Isabel Amor, executive director of equality group Iguales. "Not only will people who have a same-sex relationship be able to marry, but hundreds of children and adolescents will get recognition for their two mothers or two fathers."