The Green Party has vowed to introduce gay marriage if returned to government.
Former junior minister Ciaran Cuffe said they would push for constitutional change to allow for same-sex weddings.
"In government, the Green Party introduced the civil partnerships legislation, which goes a long way to ensuring better rights for same-sex couples," he said.
"But it is not marriage, and we believe all consenting adults, should have the option to marry."
Mr Cuffe pointed out plans were under way to introduce gay marriage in Britain seven years after civil partnership legislation was enacted there.
"I hope we in Ireland don't have to wait as long to see similar legalisation introduced here," he said.