Prime Minister David Cameron will give MPs a free vote on whether gay couples should be allowed to marry, following recent opposition from his own cabinet and ministers.
Cameron has long been supportive of the reform to allow same-sex marriages. A free vote on the proposal will allow MPs to vote according to their consciences, rather than be directed by party whips.
A number of Conservative MPs have recently expressed their concern over the proposal or shown fierce opposition.
A formal consultation to discuss how civil marriage will be reformed in England and Wales began earlier this year. Current legislation allows same-sex couples to enter into a civil partnership, but not civil marriage.
Some leading Conservatives have called for the plans to be dropped, arguing for the party to focus on other matters, such as its poor showing in the local elections and the country's struggling economy.
Children's minister Tim Loughton expressed his doubts about the issue on his website, where he wrote: "I have to say that my instinct is not to support these proposals and, as it stands, I intend to vote against measures to legalise gay marriage.
"The prime minister has clearly set out his reasons for being in favour of gay marriage and I respect his right to do so. But, I particularly respect his acknowledgement that this should be a matter of personal beliefs and that Conservative MPs, at least, will be free to make up their own minds."
Gerald Howarth, a defence minister, has welcomed the decision to hold a vote, saying after the plan was announced that it was "absolutely right and proper" for MPs to be allowed a free vote.
Defence secretary Philip Hammond has also raised doubts about Cameron's plans to introduce same-sex marriage, telling Andrew Marr: "Clearly, it is not the number one priority."
Northern Ireland secretary Owen Patterson recently become the first Tory cabinet minister to oppose Cameron's plans. In a letter to gay constituent Andrew Smith, Patterson said: "Having considered this matter carefully, I am afraid I have come to the decision not to support gay marriage."
Despite some opposition to the proposals, it is still believed the measures will go through.
Desmond Swayne, Cameron's parliamentary private secretary, recorded a video message for the cross-party Out4Marriage campaign backing the plans.
He said: "I'm married, I enjoy being married, it's a huge blessing, and therefore I want that blessing to be extended to everyone. I've come at this issue of equal marriage principally because I am a Christian."