The Communist League in Canada was founded as the Revolutionary Workers League/Ligue Ouvrière Révolutionnaire in 1977 as the result of a merger of the League for Socialist Action, the Revolutionary Marxist Group and the Groupe Marxiste Revolutionaire . Originally a Trotskyist party, the RWL was the Canadian section of the United Secretariat of the Fourth International. The group followed the US Socialist Workers Party's trajectory away from Trotskyism in favour of a view of Fidel Castro's Cuba as the vanguard of world revolution. The RWL purged members who did not support the new orientation, many of whom went on to form Socialist Challenge and Gauche Socialiste. In the late 1980s, the RWL left the USFI to become part of the new Pathfinder tendency based around the SWP. It changed its name to the Communist League in 1990. The new group ceased publication of the English Socialist Voice in favour of selling The Militant, published in New York City by the SWP.

Michel Prairie is the group's general secretary and primary spokesperson. Previous secretaries of the group are John Riddell , who was a leading figure in the LSA and the RWL, and Steve Penner , formerly of the RMG and a grandson of Jacob Penner.

The Communist League has run candidates in some provincial and municipal elections in Canada, most notably in Ontario and Quebec. John Steele was the party's nominal Ontario leader during the 1995 provincial election, and was the party's candidate for Mayor of Toronto in the 2000 election. He won 1,412 votes out of approximately 550,000 votes cast in Toronto.

In early 2004, two former leading activists in the group, Roger Annis and former leader John Riddell , left the CL over a dispute regarding protests against the US invasion of Iraq, and started the Socialist Voice website, taking the name of the RWL's old newspaper.

Today, the group has a few dozen members in Montreal, Toronto and Vancouver, and operates Pathfinder Bookstores in each of those cities.

As of the party congress held in 2000, the CL's Central Committee consisted of Carlos Catalán, Christian Cournoyer, Michel Dugré, Maria Isabel Le Blanc, Michel Prairie, and Joe Young. [1]