The RMG was formed in 1973 with the fusion of the "Old Mole" group at the University of Toronto and the Red Circle, a Marxist group that was originally in the Waffle but that remained in the New Democratic Party after the Waffle's departure. The RMG adopted the Old Mole as its journal. Subsequent to its formation, the Revolutionary Communist Tendency split from the League for Socialist Action to join the RMG.
The RMG was a sympathizing section of the United Secretariat of the Fourth International, and supported the international faction led by Ernest Mandel and Tariq Ali against the faction led by the Socialist Workers Party (US) led by Joseph Hansen and Farrell Dobbs. Its main rival, the League for Socialist Action, supported the American-led faction in the international conflict within the USFI. Where the LSA was close to the SWP, the RMG was close to Britain's International Marxist Group.
The RMG was linked with an autonomous group in Quebec with similar views, the Groupe Marxiste Révolutionnaire. In 1977, the RMG, LSA and GMR fused to form the Revolutionary Workers League/Ligue Ouvrière Révolutionnaire.