A same sex marriage referendum is to be held before the end of this Government, it was claimed.
Tanaiste Eamon Gilmore made the pledge at a party meeting this weekend, campaigners said.
The Gay and Lesbian Equality Network predicted a yes vote to pave the way for civil marriage.
Chairman Kieran Rose said: "The Government has committed to shortly bring forward legislation to recognise and support lesbian and gay headed families.
"With this urgently needed legislation in place and with the comprehensive marriage-like rights and obligations of civil partnership, civil partners including couples parenting children would have almost all the legal rights of marriage except equal status and protection in the constitution."
He said the overwhelming vote at the Constitutional Convention, the widespread celebration of civil partnerships all across the country and the growing public and political support for marriage mean Ireland is ready to move to the next step of providing access to civil marriage and full constitutional protection for lesbian and gay people and families.