Vijaya Kumaranatunga started his political life in the Lanka Sama Samaja Party. He later joined the Sri Lanka Freedom Party. He was active in the presidential campaign of Hector Kobbekaduwa in 1982. After the election, he was jailed under the emergency regulations by J.R Jayawardena for allegedly being a "Naxalite" (a political creed hitherto and henceforth unknown in Sri Lanka), but he was never charged. He contested Mahara by-election under SLFP candidature in 1983 and was maltreated by UNP supporters. An attempt was made on his life and one of his friends was killed. Vijaya won the first round of counting and a second round was ordered. At that point an infamous blackout occurred at the counting centre. By the time electricity was restored, the UNP candidate had recorded a victory by a few votes. The opposition insisted that someone had literally "eaten some of Vijaya's votes to ensure UNP victory".[6] He founded the Sri Lanka Mahajana Party (SLMP).

Hon T. B. Ilangaratne was the First President of Sri Lanka Mahajana Party. He was sworn in on May 18, 1948 beginning a three-decade long career in the Sri Lankan government. While in office, Ilangaratne helped create the Employee's Provident Fund, the National Bank, and Labor day in Sri Lanka among other things. In 1974 he served as acting prime minister.

After the passing away of leader Vijaya Kumaranatunga 1988, Chandrika Kumaranatunga lead the party for a short time.

Ahangama Withanage Oswin Nandimithra Abeyagoonasekera (known as Ossie Abeygunasekera) was a former Member of Parliament and National Organizer and the leader of the Sri Lanka Mahajana Party.

Y.P.de Silva Represented the Parliament & lead the party till 1997.
Y.P.de Silva also worked as the Deputy Minister of Foods during the period. And he has consolidated the best of his capability to Sri Lanka Mahajana Party during the time he lead.

After Y.P.de Silva's death Ranjith Navarathne got the Leadership of the Party in 1997. He did very well during his Leadership.
In 2000 General Election Ranjith Navarathne represented the Parliament through the Party for Kurunegala District. He signed the MOU of United People's Freedom Alliance in 2004. He found death on 1 May 2013.

Mr. G.M. Karunapala got the Presidentship of the Party in 2004. He did very well during his Presidentship.
In 2009 Sabaragamuwa Provincial Council Election, Mr. G.M. Karunapala represented the Council through the Party as a minister. He found death on 22nd March 2020.