Margaret Mary Ritchie, Baroness Ritchie of Downpatrick, is an Irish politician who was the Leader of the Social Democratic and Labour Party (SDLP) from 2010 to 2011. She was previously a Member of the Northern Ireland Assembly (MLA) for South Down from 2003 to 2012, and was the Minister for Social Development in the Northern Ireland Executive from 2007 to 2010. Ritchie was the Member of Parliament (MP) for South Down from 2010 to 2017. She became a life peer in 2019 initially as a non-affiliated member, and then from October 2021 as a Labour member.

The Social Democratic and Labour Party is a social-democratic and Irish nationalist political party in Northern Ireland. The SDLP currently has seven members in the Northern Ireland Assembly (MLAs) and two members of Parliament (MPs) in the House of Commons of the United Kingdom.