In the late early 1950s, the LSSP spearheaded the 1953 Hartal strike, caused by vast food price inflation under the United National Party (UNP) government.

During this period, the party was able to use its considerable political influence to reform the former British colony of Ceylon into a socialist republic by nationalising organisations in the banking, education, industry, media and trade sectors.

Through their election landslide in 1964, the United Front brought the world's first non-hereditary female head of government in modern history, Sirimavo Bandaranaike to power as Prime Minister of Sri Lanka.

[5] The Lanka Sama Samaja Party was founded on 18 December 1935, with the broad aims of Sri Lankan Independence and Socialism, by a group of young politicians.

[6][7] The group at the foundation numbered a bare half-dozen, and composed principally of students who had returned from study abroad, influenced deeply by the ideas of Karl Marx and Lenin.

[9][10][11] The LSSP grew out of the Youth Leagues of Ceylon – societies of young people, mainly intellectuals, who wanted independence for the British ruled Sri Lanka – in which a nucleus of Marxists had developed.

[17] The Youth Leagues campaigned for independence from Britain, notably organising opposition to the so-called 'Ministers' Memorandum', one which in essence called for the colonial authorities to grant increased power to local ministers.

[19][20] The mills; the island’s largest textile factory at that time with 1,400 workers (two-thirds of Indian origin and one-third Sinhalese), gave the members of the Youth League a chance for leadership as well as experience in trade union agitation.

[22] In 1933 the group got involved in the Suriya-Mal movement, which had been formed to provide support for indigenous ex-servicemen by the sale of Suriya (Portia tree) flowers.

[33] In 1937, the British Colonial Governor Sir Reginald Stubbs attempted to deport a young Anglo-Australian planter, Mark Anthony Bracegirdle, who had joined the LSSP.

[41] In 1940, the Lanka Estate Workers' Union (LEWU) intervened in a strike at Mooloya, becoming the harbinger of a wave of trade-union action on the plantations.

[76][77] Only Colvin R. de Silva, Leslie Goonewardene, Vivienne Goonewardena and Selina Perera succeeded in evading arrest up to the end.

I do not believe that anyone claiming to be a Statesman would ask us to accede to a bill of this nature ... We cannot proceed as if we were God's chosen race quite apart from the rest of the world; that we and we alone have the right to be citizens of this country.

[108][109][110] At the 1952 general election, the electoral performance was harmed by the relative prosperity due to the price of natural rubber being driven up by the Korean War.

[131] In 1956 the LSSP went into a no-contest pact with the Mahajana Eksath Peramuna (People's United Front) of SWRD Bandaranaike, which he had formed with Philip Gunawardena and the VLSSP.

[136][137][138] In July 1959, both LSSP and the Communist Party withdrew their support for the government, as inner-party feuds within the SLFP had resulted in a temporary victory for the right-wing and expulsions of leftist ministers like Philip Gunawardena.

[141][142] The votes won by the LSSP, the Communists and the Mahajana Eksath Peramuna (a new party, not the 1956 front) of Philip Gunawardena, were sufficient to have made them the biggest bloc in Parliament.

[143][144] Elections were held again in July and the LSSP had a no-contest pact with the Sri Lanka Freedom Party (SLFP) of Sirimavo Bandaranaike, which was thus able to form a government.

[153] The front launched agitations on issues like bring down the prices of essential commodities, leading it to represent an immediate threat to the governance of SLFP.

[115] In 1964, the LSSP held a conference at which the majority agreed with a theoretical categorisation of the SLFP by Hector Abhayavardhana as a petty bourgeois party, leaving the door open to a united front with it.

[173] The Party was able to advance parts of its programme considerably: Foreign-owned plantations were nationalised, local ownership was restricted, democratically elected workers' councils were established in state corporations and government departments under the purview of its ministries, and measures were taken that narrowed the gap between the rich and poor.

[180] The SPC, which became a model for the Third World and remains so today, was based on a report on Pharmaceuticals in Sri Lanka of which the authors were Dr S. A. Wickremesinghe and Seneka Bibile.

[182][183] Leslie Goonewardene, easily the most cosmopolitan of the party's leaders, established contact with the 'Captains' of the Movement of the Armed Forces ('Movimento das Forças Armadas' - MFA) of Portugal, after the Carnation Revolution of April 1974; he also became a theoretician of Eurocommunism and its application to Sri Lanka, writing a pamphlet 'Can we Get To Socialism This Way'.

[189] This was finally formed in 1977 with the CPSL and with the People's Democratic Party (PDP), made up of leftist elements from the SLFP led by Nanda Ellawala.

[193] The same year the LSSP suffered another split, as a group led by the youth leader Vasudeva Nanayakkara broke away and formed the Nava Sama Samaja Party (NSSP).

Anil Moonesinghe, Cholomondely Goonewardena, G. E. H. Perera, Wilfred Senanayake and others formed the Sri Lanka Sama Samaja Party (SLSSP), which dissolved the next year and merged with the SLFP.

[204][page needed] At the Presidential election held that year, the LSSP put forward Dr Colvin R de Silva as its candidate, the SLSSP backed Hector Kobbekaduwa of the SLFP.

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

[216][217][218][219] On 4 December 2019, Tissa Vitharana was appointed as Governor for the North Central Province, Sri Lanka,[220] being sworn in before President Gotabaya Rajapaksa.

[241][239] In the period of underground struggle, the Kamkaruwa, was revived as a legal Sinhalese weekly the 'open' section of the Party and published until banned by Admiral Sir Geoffrey Layton.