The first same-sex marriages in England and Wales took place following the passage of the Marriage (Same Sex Couples) Act 2013.

Same-sex marriage is legal in all parts of the United Kingdom. As marriage is a devolved legislative matter, different parts of the United Kingdom legalised at different times; it has been recognised and performed in England and Wales since March 2014, in Scotland since December 2014, and in Northern Ireland since January 2020. Civil partnerships, which offer most, but not all, of the rights and benefits of marriage, have been recognised since 2005. The United Kingdom was the 27th country in the world and the sixteenth in Europe to allow same-sex couples to marry nationwide. Polling suggests that a majority of British people support the legal recognition of same-sex marriage.

• Legislation to allow same-sex marriage in England and Wales was passed by the Parliament of the United Kingdom in July 2013 and took effect on 13 March 2014. The first same-sex marriages took place on 29 March 2014.
• Legislation to allow same-sex marriage in Scotland was passed by the Scottish Parliament in February 2014 and took effect on 16 December 2014. The first marriage ceremonies for same-sex couples previously in civil partnerships occurred on 16 December. The first marriage ceremonies for couples not in civil partnerships occurred on 31 December 2014.
• Legislation to allow same-sex marriage in Northern Ireland was passed by the Parliament of the United Kingdom in July 2019 and took effect on 13 January 2020. The first same-sex marriage ceremony took place on 11 February 2020.

The Marriage Act 2013 is an Act of the Parliament of the United Kingdom which introduced same-sex marriage in England and Wales.