Only 6 percent said they were undecided, the Irish Independent reported. Eighteen percent said they are against allowing same-sex couples to wed.
The survey conducted by RedC Research and Marketing for Paddy Power found that support was highest among women, people younger than 44 and those living in Dublin and the commuter belt around the capital. Labor Party supporters were also more likely to favor gay marriage, although majorities in Fine Gael and Fianna Fail support it.
A referendum on the issue is expected to be held in 2015. Prime Minister Enda Kenny said earlier this week he would campaign for passage of the referendum, coming out on the issue for the first time.
The Catholic bishops released a statement on the other side.
RedC surveyed 1,004 adults by telephone Monday, Tuesday and Wednesday.
Gay marriage is now legal in much of Europe. While Ireland, influenced by its powerful Catholic church, has tended to be more socially conservative, public opinion has shifted on many issues in recent years.