It was formed through the expulsion from the Lanka Sama Samaja Party (LSSP) of the Vama Samsamja tendency led by Dr Vickrambahu (Bahu), Sumanasiri Liyanage and some others.

In 1976 when the LSSP was thrown out of the coalition large numbers joined the tendency and in December 1977 it declared itself as Nava Sama Samaja Party.

Initially the NSSP was affiliated with the Committee for a Workers' International but, in the opinion of the CWI, never fully agreed with the analysis that it had made of Stalinism, of developments in the former colonial and semi-colonial world and the national question.

Since 1991 the NSSP, led by Vikramabahu Karunaratne, has been the Sri Lankan section of the Fourth International alongside other Samasamaj parties.

[2] In October 2020 Executive Bureau of the Fourth International released a statement condemning the NSSP for allying with the United National Party (UNP) in 2020 Sri Lankan parliamentary election.