Alan Duncan is to become the first Conservative MP to enter into a civil partnership - often described as a "gay wedding" - later this year.
Alan Duncan and James Dunseath plan a summer ceremony
The shadow business secretary, 50, proposed to James Dunseath, 39, a press officer in the City, on 14 February while the pair were on holiday in Oman.
"James joked that if I had not asked him on Valentine's Day, he would have asked me on Feb 29," Mr Duncan said.
Tory leader David Cameron said he was "thrilled" for Mr Duncan.
The UK has allowed civil partnerships, the legally recognised union between two people of the same sex, since December 2005.
The most well-known couple to take advantage of the legislation are Sir Elton John and his partner David Furnish, who "tied the knot" on 21 December, 2005.
Mr Duncan, who announced his betrothal in the Daily Telegraph's Court & Social page, is the first Tory MP to enter into a civil partnership.
"I never ever imagined that one day I would be a beneficiary of the legislation," he said.
"What James and I are entering into is not a marriage, it is a civil partnership.
"You could not find two more conventional people to enter into a civil partnership."
The couple met at a dinner given by mutual friends 14 months ago.
Mr Dunseath told the Daily Telegraph: "It's just fantastic. We hit it off instantly and our friends say we are inseparable.
"He may be a politician but he's great fun. We both feel it's so right and we're very lucky."
Mr Cameron, who began his leadership pledging support for gay partnerships, said he hoped to attend Mr Duncan and Mr Dunseath's civil partnership ceremony at Marylebone registry office in the summer.
He told the Daily Telegraph: "I am absolutely delighted for Alan and James and wish them all the very best."