Peter Gary Tatchell (born 25 January 1952) is an Australian-born British human rights activist, who gained international celebrity for his attempted citizen's arrest of Zimbabwean President Robert Mugabe in 1999 and 2001, on charges of torture and other human rights abuses.

Tatchell was selected as Labour Party Parliamentary candidate for Bermondsey in 1981, and was denounced by party leader Michael Foot for supporting extra-parliamentary action against the Thatcher government; though the Labour Party subsequently allowed his selection, when he ran in the Bermondsey by-election in February 1983. In the 1990s, he became a prominent gay equality and LGBT campaigner through the direct action group OutRage!, which he co-founded. He has tackled a wide variety of human rights issues, and is a frequent contributor on such subjects in print and through broadcast media authoring thousands of articles and six books. In 2006, New Statesman readers voted him sixth on their list of "Heroes of our time".

He was named Campaigner of the Year in The Observer Ethical Awards 2009.