[2] The KPL was founded on 2 January 1921, in the town of Niederkorn, making it one of the oldest parties in Luxembourg.

In 1937, the Bech government attempted to introduce the so-called Maulkuerfgesetz ("Muzzle law") which would have banned the party.

Following the end of the Second World War, the party, which won 11.1% in the legislative elections, joined the National Union Government (1945–47).

[3] In legislative elections held in the same year, the party registered 10.4% of the vote, and won five of the Chamber of Deputies' 56 seats.

After disputes between a majority within the Left and leading KPL members shortly before the 2004 elections the party again ran separate lists.