Peter Taaffe (7 April 1942 — 23 April 2025) was a British Marxist Trotskyist political activist and a longtime leader of the Socialist Party and its predecessor, the Militant tendency.
Taaffe was the founding editor of the Trotskyist Militant newspaper in 1964, and became known as a leading member of the entryist Militant group. Taaffe was expelled from the Labour Party in 1983, along with four other members of Militant's editorial board.
Taaffe was influential in the policy decisions of Liverpool City Council of 1983–1987, according to the council's deputy leader Derek Hatton, and in the formation of the Militant tendency's policy regarding the Poll Tax in 1988–1991.