Junior minister Barbara Follett has been moved to the Department for Culture, Media and Sport.
She was previously a key minister working on the Equality Bill.
Ms Follett was a Work and Pensions minister in addition to her equality responsibilities.
The Equality Bill is expected to form part of the Queen’s Speech, the government’s programme for the forthcoming session of Parliament, which will be presented in December.
It includes proposals for all public bodies to promote equality for gay and lesbian people.
The Bill is intended to be an extension of the current duty on public authorities to actively promote equality into services like fostering, magistrates courts and health clinics and to make their services more accessible to lesbian, bisexual and gay people.
It has not been announced who will replace Ms Follett, 65, as Equalities minister.
She was a strong supporter of LGBT History Month, attending the pre-launch event in 2007, and the International Day Against Homophobia.
The MP for Stevenage since 1997, she is married to novelist Ken Follett.
Mrs Follett was Parliamentary Private Secretary to Tessa Jowell as Minister for Women from 2005 to 2006 and as Secretary of State for Culture, Media and Sport from 2006 to 2007.
She was Parliamentary Private Secretary to Ruth Kelly as Minister for Women from 2006 to 2007.
Mrs Follett will replace Margaret Hodge at DCMS, who is leaving government for family reasons.
The return of Peter Mandelson, the only openly gay EU Commissioner, to frontline British politics as Business Secretary has been the main story of Gordon Brown’s reshuffle, which began on Friday.
Nick Brown, unlike Mr Mandelson a close ally of the Prime Minister, has been promoted to Chief Whip, but he will not be a member of the Cabinet.
Mr Mandelson’s appointment means that for the first time since 2001 that there is a gay person in the Cabinet.
Mr Brown will attend Cabinet as Chief Whip.