A Sinn Fein motion calling on the Northern Ireland Executive to legislate to allow for same sex marriage has been defeated in the assembly by 53 votes to 42.
Those against the motion included 50 unionist MLAs and three members of the Alliance.
Those in favour included all 37 nationalists who voted and three unionists.
An Alliance Party amendment was also defeated.
It would have emphasised the freedom of churches to practise and define marriage as they choose.
After the amendment was rejected, the Alliance leader David Ford and two of his party colleagues abstained on the main motion.
Proposing her party's motion, Sinn Fein assembly member Bronwyn McGahan said she respected there were deeply held religious, cultural and personal views surrounding the issue.
"MLAs, regardless of religious belief, represent every section of our community, including our LGBT (lesbian, gay, bisexual and transgender) members and this motion is about ensuring marriage equality for everyone regardless of their sexual orientation," she said.
"What churches do is a matter for churches but the state needs to treat everyone with equality."
Finance Minister Sammy Wilson, of the DUP, defended his party's use of the petition of concern saying it was important to stop "reckless legislation".
He said the motion would not promote safeguards or equality and he did not believe a balance of opinions had been accurately reflected during the debate.
"This is not an issue of equality, it is an issue of redefining marriage as it has always been understood, " he said.
"Once there's a change in the legal definition of marriage then those who take up contrary views will find themselves up against the law - their rights will be infringed."
He also said the motion's reference to a vote at the Irish constitutional convention had no bearing on the Northern Ireland Assembly.
The Sinn Fein motion had said it welcomed the 79% majority vote at the Irish convention on the constitution in favour of marriage equality.
Colum Eastwood of the SDLP said he believed that if two people of the same gender loved each other and wanted to commit their lives together they should be supported.
Alliance Party leader David Ford spoke on his party's amendment, which stated its support for the extension of civil marriage provisions in Northern Ireland to same-sex couples provided that faith groups were respected.
"Equal marriage is a matter of great importance to many in our community, to many citizens who have a legitimate expectation that they will be treated equally by the state, but I also acknowledge that it's an issue of great sensitivity and of huge significance for a number of religious denominations and other faith groups," he said.
Mr Ford said the Sinn Fein motion was "grandstanding and futile" as it was not balanced in its support for same-sex marriage compared with religious freedom.
"The Executive is not going to legislate in this term for equal marriage even if the house had passed the motion," he said.
Ulster Unionist assembly members spoke in a personal capacity as the party allowed for a vote of conscience on this matter.
Newry and Armagh MLA Danny Kennedy said he was opposed to any change in legislation due to his religious beliefs which he said were consistent with the teaching of the Presbyterian Church.
He said Sinn Fein were "guilty of engaging in a very cynical, political exercise which is of no benefit to any section of our community, not least the LGBT."
The amendment and the motion both fell.