Parallel bills aimed at introducing same-sex marriage in Northern Ireland are set to enter the House of Commons and House of Lords this week.
It was announced last week Northern Ireland-born Labour MP Conor McGinn would be put his Marriage (Same Sex Couples) (Northern Ireland) Bill before the House of Commons on Wednesday.
Conservative peer Lord Hayward will put his identically-titled bill before the House of Lords on Tuesday afternoon.
On the day the Bill is put before the House of Commons, a 30,000-strong petition organised by the LGBT campaign group Love Equality will be placed before 10 Downing Street calling for the Government's support for legislation change in Northern Ireland.
Lord Hayward said: “It gives me great honour to launch the Westminster campaign for equal marriage rights in Northern Ireland in the House of Lords.
“I am pleased to introduce the Marriage (Same Sex Couples) (Northern Ireland) Bill in the Lords with the support of the Love Equality campaign from Northern Ireland.
"The strength of public opinion for equal marriage rights in Northern Ireland will be shown by the petition they are due to present to Downing Street later this week.
“I am particularly delighted to launch the Bill in the presence of Ulsterman John Henry, whose powerful story moved me and so many others in recent weeks.”
John Henry - brother of Ulster and Ireland rugby star Chris Henry - told the Belfast Telegraph in February of his regret at the way his brother had found out he was gay.
Patrick Corrigan, Amnesty Northern Ireland programme director and a member of the Love Equality campaign, said: “We welcome this important intervention by Lord Hayward.
"Our preference has always been for the Northern Ireland Assembly to pass marriage equality legislation, in line with the overwhelming support which exists among the public here.
“However, without functioning devolution for the last 15 months, we now look to Westminster to legislate."
Northern Ireland remains the only part of the United Kingdom where marriage for same-sex couples is banned.
In 2015, a majority of MLAs in the Stormont Executive voted to support equal marriage but were blocked by the DUP's controversial use of the Petition of Concern.