Councillors are set to lead key debates on the equality issue in June.
The move follows the yes vote for equal marriage during the referendum in Ireland last week and is the latest action by Alliance in moving the debate forward in Northern Ireland.
Alliance Councillor Emmet McDonough-Brown said: “Ireland’s result last week has left Northern Ireland out of step on equality issues. As it stands a same sex couple can now legally marry in all other parts of the UK and Ireland and the LGBT community should also have the same rights here.
“The Alliance Party is committed to delivering a shared society for everyone, based on civil and religious liberty and equality for all – regardless of age, gender, disability, race, ethnicity or sexual orientation – and has continually led the way on LGBT issues, including adoption and tackling homophobic bullying in schools.
“Alliance supports the extension of state provided civil marriage to same sex couples, while recognising protections are needed for those faith groups that wish to continue to observe and practise marriage within their beliefs.”