Former Ulster Unionist MP Ken Maginnis has quit the party after 50 years.
The party leadership had distanced itself from Mr Maginnis when he referred to gay marriage as "unnatural and deviant behaviour".
He later insisted he stood by his remarks, referring to "unnatural physical acts" by "deviants".
"These are people that seem to take some pride expressing their particular rights. I disagree with those rights and that deviance," he added.
Party leader Mike Nesbitt and senior party members were clearly embarrassed by his attack and today he said it was time to leave.
Mr Maginnis, 74, from Dungannon, Co Tyrone, and the former MP for Fermanagh-South Tyrone said: "I have agonised over the last three months. Currently there is no room for independent or logical thinking (within the party) and that does not suit me."