Chile's Movement for Homosexual Integration and Liberation charges in the suit that barring gay marriage violates several parts of the American Convention of Human Rights, the Santiago Times reported.
Alberto Roa, general secretary of the group, said the lawsuit is the first of its kind and was presented to the Inter-American Commission of Human Rights.
The commission obliges states to "respect every recognized right and liberty" and to "guarantee them to every person subject to its jurisdiction, without discrimination," Roa said.
"We are demanding the legalization of marriage and civil union, not just because we all want to get married," he said. "This is a matter of equality for us."
The lawsuit was filed by attorneys Ciro Colombara and Hunter T. Carter, a former aide to U.S. Secretary of State Hillary Clinton.