Tim Loughton said the Government could face penalties and fresh legal challenges if it ignores a Supreme Court ruling that the Civil Partnership Act 2004 - which only applies to same-sex couples - was incompatible with the European Convention on Human Rights.
The ruling follows a long campaign by London couple Rebecca Steinfeld, 37, and Charles Keidan, 41, to change the law.
Mr Loughton called on Theresa May to respond by committing to amending his private members’ Bill on the issue on July 18 to extend civil partnerships to heterosexual couples who do not want to get married.
He also stressed that Equalities Minister Penny Mordaunt has already ruled out scrapping civil partnerships to comply with the court ruling, leaving extension as the only option.
There are only a “handful” of MPs who would oppose the idea for religious reasons and “if there was a free vote in the Commons it would cruise through”, he added.
The East Worthing and Shoreham MP said he was “elated” with the court ruling, telling The Yorkshire Post: “It was a pretty emphatic ruling, England margins of 5-0, basically saying that they have no excuse of playing for more time so basically there’s no excuse of playing for more time, so effectively they’ve got to some up with an urgent resolution of it.
“Penny Mordaunt has said on record that, and she supports all this anyway, that she’s not in favour of scrapping civil partnerships as a way of resolving it.
“So that would indicate there’s only one way to go, so basically there’s no excuse for the Government not now getting on with that.”
He went on: “The way the ruling was framed this morning it makes it virtually impossible to ignore it.
“They would be absolutely in breach of the convention if they said ‘oh we’ll think about it’.
“And particularly given that my Bill available in Parliament, there is an obvious vehicle for them to latch the change on to.
“They haven’t got to create something completely new, so if they don’t do something within say six months then I think there would be very strong grounds for going back to court.”
He added: “This time next year, (straight) people should be able to form civil partnerships.”
At Prime Minister’s Questions, Mrs May said the Government was "well aware" of its legal obligations, adding: "We'll obviously need to consider the judgment of the Supreme Court with great care but we also recognise the very sensitive and personal issues that are involved in this case and we acknowledge the genuine convictions of the couple involved."
Mrs May added that the Government had already "committed to undertake a full review of the operation of civil partnerships".
Shadow Equalities Minister Dawn Butler said: “The Government should have already legislated to ensure all couples have equality of choice. Now the Supreme Court case has ruled the current law is discriminatory and a violation of human rights, the Government must no longer stand in the way of progress.
“Labour is calling on the Government to take action and change the law to ensure all people have access to civil partnerships and are able to choose what is right for them.”
Later, Mrs May's official spokesman refused to commit to extending civil partnerships, reiterating the review which is underway.
He could not say whether the review would report back in time for the committee stage of Mr Loughton's Bill on July 18.