Marxist Worker was a Trotskyist organisation in Britain, which produced a publication of the same name. It was formed by the Bolton branch of Workers' Fight, who opposed that organisation's merger with Workers' Power in 1976 and refused to enter the new organisation, the International-Communist League. The group also had supporters in Wigan.
The Marxist Worker group merged with the International Marxist Group later in the 1970s. Some members instead joined Big Flame, the IMG's partner in the Socialist Unity electoral bloc.