Bachelet signed the proposal, which will be sent to lawmakers, at a ceremony in the presidential palace. She said the measure seeks to expand the definition of marriage between a man and a woman and would also expand rights for gay couples, allowing them to adopt children.
“We can’t let old prejudices be stronger than love,” Bachelet said.
Chile approved civil unions for same-sex couples in 2015 and decriminalised gay sex in 1999. The bill comes a week after Chile’s Constitutional Court upheld a measure that would end the country’s absolute ban on abortions.
Civil unions have been recognised in several South American countries, though only Argentina and Uruguay have codified same-sex marriage. Gay marriage has also been legalised in Brazil and Colombia under court rulings.