In the 2004 legislative election, the party was part of the United People's Freedom Alliance that won 45.6% of the popular vote and 105 out of 225 seats.

In 1952 Wickremesinghe's wife, the English-born Doreen Young Wickremasinghe, a former leader of the Suriya-Mal Movement, was elected to the Sri Lankan parliament.

The ULF broke down in 1964 when the then Prime Minister Sirimavo Bandaranaike offered ministerial posts to LSSP and the CP.

However, one faction of the party, led by S. A. Wickremasinghe and Indika Gunawardena, maintained a line of critical support for the government.

When SLFP shelved the PA and formed the United People's Freedom Alliance together with Janatha Vimukthi Peramuna ahead of the 2004 elections, CPSL and LSSP initially stayed out.

[3][4] During the 2020 Parliamentary elections, the CPSL put forward two candidates, Mahesh Almedia in Colombo and Weerasumana Weerasinghe in Matara, under the SLPP's Pohottuwa symbol.

The CPSL and other Leftist parties were framed by the J R Jayawardane government for instigating 1983 Black July pogroms against the Tamil people.