CPI (ML) originated from the "Internationalists in Ireland", a group started on 9 December 1965 by Hardial Bains, while he was working as a microbiologist at Trinity College, Dublin.

[2] His efforts culminated in the "Necessity for Change" conference, at which delegates from Canada, India, Ireland and Britain pledged to build Marxist–Leninist parties in their countries.

[3] In 1968, the Internationalists came to public attention as they organised a protest against the visit of King Baudouin of Belgium to Trinity College.

[24][3][25] The CPI (ML) supported armed struggle for the reunification of Ireland and initiated the Spirit of Freedom Committee to work with Irish republicans.

[30] With the collapse of socialism in Albania, the CPI (ML) opened up relations with the Workers' Party of Korea and signed the 1992 Pyongyang Declaration.

Following the group's dissolution, former leading member Brendan Doris stood in the 2011 Dublin West by-election for An Chomhdháil Phobail/The People's Convention (CPPC),[33] achieving 95 first preference votes.