All but three members of Parliament voted to pass the legislation, which says couples who have a relationship registered under the Relationships Act can adopt children unknown to them, the Australian Broadcasting Corp. reported Thursday.
Upper House Member of Parliament Craig Farrell said the bill doesn't favor same-sex couples over any others.
"It gives them the ability to apply, and it is then up to the authorities to say what is in the best interests of the child," he said. "It is really a pretty straight-forward piece of legislation."
Supporters of the law applauded its passage.
"Today is a proud day for Tasmania, for we have removed the very last vestige of discrimination against same-sex couples in existing state law," said Gay and Lesbian Rights Group spokesman Rodney Croome.
The Save the Marriage Coalition, which opposes the bill, said the legislation focuses too much on the rights of adults, not children.
"The bill will relegate some Tasmanian children to a life without mothers or a life without fathers," said Guy Barnett, the spokesman for the organization.