The Adoption Amendment Bill passed the Legislative Council 10 votes to three yesterday, with MLCs from all sides of politics speaking in favour of the change.

It updates 1998 laws to allow any couple that has been in a registered relationship for more than three years to apply to adopt a child, even if that child is not related to either party.

This means same-sex couples would be able to adopt their foster child, if that was an option for that child.

The existing law required that a couple be married for at least three years before being eligible to adopt.

The reform builds on changes made in 2003, which allowed people in both heterosexual and same-sex registered relationships to legally adopt their partner's child.

Gay rights advocate Rodney Croome said the legislation was a significant win for equality in Tasmania.

``This completes a long process that began with the decriminalisation of homosexuality in 1997, and now finally, after 16 years, all discrimination in existing Tasmanian law has been removed,'' Mr Croome said.

Save Marriage Coalition spokesman and Lyons Liberal state candidate Guy Barnett said the legislation would disadvantage children by denying them either a mother or a father.

Launceston independent MLC Rosemary Armitage, Windermere independent MLC Ivan Dean and Montgomery Liberal MLC Leonie Hiscutt voted against the legislation.

Ms Armitage said she could not support the legislation while there were no long-term studies to show that being raised by same-sex parents was not damaging to children.

``We now say sorry to what we call the Stolen Generation, and I am sure at that time we believed it was for good reasons and in the best interests of the children that they be adopted,'' Ms Armitage said.

Pembroke Liberal MLC Vanessa Goodwin was among those who supported the legislation.

``I would much rather have a child being raised in a stable, loving, same-sex family than in a dysfunctional heterosexual family unit  where the children are being abused or neglected,'' Dr Goodwin said.