Liberal Democrat Lynne Featherstone has been appointed a junior Home Office minister with responsibility for equality, she said today.
Ms Featherstone, who was equality spokeswoman for two years, said it was a "huge opportunity to change things for the better".
She wrote about the appointment on her blog ahead of the official announcement from Downing Street.
The MP for Hornsey and Wood Green will work under Conservative Home Secretary Theresa May, who is also Minister for Women and Equality.
Ms Featherstone wrote: "For two years as shadow equalities spokesperson - through the Equality Bill, through countless speeches to groups, through our conference policy papers on women and youth - it has always been about what Lib Dems would do about equality if we were in Government. Blimey - we are!
"Now I can deliver it - well some of it. Equalities was not in that first tier agreement released by Liberal Democrats and Conservatives prior to coalition - but it will be part of the second tier agreement I believe.
"So - today will find out the lie of the land - but the chance to deliver Liberal Democrat equality policy is phenomenal.
"Will I get our whole agenda agreed? Well I might - but there are a few things I can see causing ructions - but I am optimistic about most of it."
Downing Street is expected to unveil a raft of junior ministers later today.
It is understood that Tory Nick Hurd, son of former foreign secretary Lord Hurd, will keep his portfolio from the opposition front bench to become Charities Minister.
Lib Dem Alistair Carmichael will be Senior Government Whip in the new administration, a party source said.
He will also act as the Lib Dem Chief Whip in the coalition, the source indicated.
Mr Carmichael was the Lib Dems' spokesman on Scottish and Northern Irish affairs in the last parliament.
Tory Patrick McLoughlin has already been confirmed as the Government's Chief Whip.
Conservative Jonathan Djanogly said he had been appointed junior justice minister.
He told his Twitter followers: "I am delighted to have been appointed as a Parliamentary Under Secretary of State at the Ministry of Justice."
Mr Djanogly previously served as shadow business minister and shadow solicitor general.