Shadow chancellor Ed Balls said he is "really pleased" that David Cameron is backing same-sex marriage.
Speaking as one of the guests on ITV's The Agenda with Tom Bradby, Mr Balls said he admired the PM for defying sections of the Conservative Party on the issue.
"I think it's brave, and he's divided his party in quite a deep way," he added.
The Agenda with Tom Bradby airs at 10.35pm tonight on ITV.
Other guests on tonight’s programme are columnist Amanda Platell, writer Anthony Horowitz and broadcaster Mariella Frostrup.
Landmark plans to legalise gay marriage got the green light in the Commons, despite a majority of Tories failing to support the Government.
The Prime Minister will read the letter delivered to Number 10, take their views on board, but not change his mind over gay marriage.
Many Conservative MPs just do not understand the move when the tax measure is in the Coalition Agreement.