A proposed Westminster law for same-sex marriage in Northern Ireland will be introduced at the end of March.
South Armagh-born Labour MP Conor McGinn said he would table a private member’s bill.
Northern Ireland Secretary Karen Bradley has previously said MPs would be given a free vote.
It follows the collapse of talks to restore the Stormont devolved institutions, where the DUP remain firmly opposed to the measure.
Mr McGinn said: “My preference is for a fully functioning Executive and Assembly to deal with this issue, but LGBT couples in Northern Ireland should not be made to wait a moment longer for their basic rights.
BREAKING: Love Equality welcomes Northern Ireland equal marriage Private Member's Bill. We are happy to be working with @ConorMcGinn MP to prepare the Bill and build support across Parliament. https://t.co/kiTz3kq5vL pic.twitter.com/UhaHT05Ve0— Love Equality NI (@Love_EqualityNI) February 23, 2018
“That is why I am introducing this Bill at the earliest available opportunity. It will test the mood of the House of Commons and I am very confident that we will win any vote. It is then for the Government to legislate.
“If my constituents in St Helens can marry the person they love, just like people in London, Edinburgh, Cardiff and Dublin, then I don’t see why couples in Belfast should not be able to do the same.”
Patrick Corrigan of the Love Equality campaign for civil marriage equality said he would work closely with Mr McGinn in preparation of the private member’s bill.
He added: “We will be working to build support for the Bill from MPs across the UK and are confident of a convincing majority in favour.
“We now look to Parliament to uphold the rights of people in Northern Ireland and to respond to overwhelming public support here.
“However, the rights of LGBT people in Northern Ireland to be treated equally should not be left to the Private Member’s Bill process.
“We repeat our call on the UK Government to introduce legislation to bring Northern Ireland’s laws on marriage equality into line with the rest of the UK and Ireland.”
The Love Equality campaign for equal civil marriage in Northern Ireland is led by the Rainbow Project, Amnesty International, Irish Congress of Trade Unions and other civic organisations.