Conservative MP Daniel Kawczynski, who came out as bisexual at the weekend, voted against the Equality Act in 2007, but did support the same-sex marriage bill at second and third reading of this year in the Commons.
The MP for Shrewsbury and Parliamentary Private Secretary to Welsh Secretary and equal marriage opponent David Jones revealed that he had told his Conservative association he was now in a relationship with a man in an interview to the Telegraph at the weekend.
The announcement makes him the first Tory MP to openly identify as bisexual.
Mr Kawczynski has one daughter and separated from his wife in 2011.
The MP previously voted in favour of an amendment to the Human Fertilisation and Embryology Bill in 2008 requiring the need for both a father and a mother to be considered when taking account of the welfare of a child who could be born as a result of fertility treatment.
In 2007 Mr Kawczynski voted against the Equality Act, which bans discrimination and harassment on the grounds of sexual orientation.
He decided to vote in favour of the bill, telling activists he was motivated by “convictions as a God-fearing man, and as an individual that believes equality for all”.