Nick Herbert has resigned from government as the policing minister in the wake of David Cameron’s reshuffle.
It’s understood the 49-year-old was not happy with being moved to a different job.
In the past hour, Mr Herbert tweeted that he will now “focus on new ideas & protecting countryside” outside of government.
The move is a surprising development, as the Conservative junior minister had been tipped for promotion to the top tier of the cabinet.
Mr Herbert is a keen supporter of equal marriage and has strongly criticised religious opponents in recent months for criticising the measure.
He said the Church of England’s current position made him feel “distant” from his own Christian faith.
Mr Herbert entered into a civil partnership with Jason Eades in 2009 and said it was unfair that they could not marry: “The longer this debate has gone on, the more strongly I have felt about it.
“I am getting fed up with people metaphorically jabbing a finger in my chest and saying, ‘You should put up with a civil partnership’”.
Mr Herbert was seen marching with members of the Conservative Party’s LGBT campaign group at last weekend’s Brighton Pride.
In other reshuffle developments, junior minister Chris Grayling has replaced veteran heavyweight Ken Clarke as justice secretary.
The appointment is likely to be treated with caution by some in the LGBT community.