The newly appointed defence secretary previously voted against allowing same-sex marriage for armed forces personnel outside of the UK.
That vote, which pitted him against the majority of MPs in the House of Commons, is one of two times Gavin Williamson has voted to deny marriage rights to gay people.
He was one of a minority of MPs who voted against the overseas marriage (armed forces) order in 2014, which would have allowed gay serving armed forces members to get married overseas.
A year earlier, Williamson joined with 134 of his Conservative party colleagues in the House of Commons to vote against legislation that made same-sex marriage legal in the UK.
Despite Williamson's votes, both laws were passed.
According to reports, Williamson also led the talks with social conservatives in Northern Ireland's Democratic Unionist Party to secure an agreement for Theresa May to form a government after she lost her majority in the snap election she called earlier this year.
He was named defence secretary on Thursday in the wake of the shock resignation of Sir Michael Fallon amid sexual harassment claims in Westminster.
The MP for South Staffordshire was promoted from chief whip to the cabinet position, leaving several Conservative MPs shocked that he'd leapfrogged others into the senior post.
Williamson's views on same-sex marriage run counter to those of May, who said she was committed to equality for LGBT people in the UK during her leadership campaign last year.
"When I launched my campaign for the leadership I set out my belief in building a country that works for everyone," May said. "Central to that vision is a commitment to equality, and I will always stand up for the rights of LGBT people.
"I supported civil partnerships in 2004, and was proud to sponsor the legislation that introduced full marriage equality in 2013 because I believe marriage should be for everyone, regardless of their sexual orientation."
Mark Di Stefano is a Media and Politics Reporter for BuzzFeed News and is based in London.
Contact Mark Di Stefano at email@example.com.
Got a confidential tip? Submit it here.