The Sri Lanka Freedom Party (SLFP; Sinhala: ශ්‍රී ලංකා නිදහස් පක්ෂය, romanised: Śrī Laṁkā Nidahas Pakṣaya; Tamil: இலங்கை சுதந்திரக் கட்சி, romanised: Ilaṅkai Cutantirak Kaṭci) is a centre-left political party in Sri Lanka. Founded by S. W. R. D. Bandaranaike in 1951, the party was one of Sri Lanka's two main parties from the 1950s to the 2010s, serving as the main rival of the centre-right United National Party. Following a split in the late 2010s and subsequent electoral losses, the influence of the party has since diminished.

The party is generally considered as having a democratic socialist or progressive economic agenda and is often associated with Sinhalese nationalist parties. The party follows a non-aligned foreign policy but has historically had close ties to socialist nations.

The Sri Lanka Freedom Party was founded in 1951, when long-standing United National Party stalwart S. W. R. D. Bandaranaike defected from the party and crossed over to the opposition with several of his other close associates. His party, the Sinhala Maha Sabha, was dissolved and the Sri Lanka Freedom Party was inaugurated.

After Sri Lanka gained its independence, the SLFP represented a form of non-revolutionary socialism and a policy of non-alignment with strong ties to socialist countries. Its social democratic and nationalist policies in the aftermath of Sri Lankan independence supported its rapid rise towards attaining major party status alongside the centre-right United National Party. SLFP founder S. W. R. D. Bandaranaike stated that the basis of the party would be the 'Pancha Maha Balavegaya' (Five Great Forces) which consisted of the native doctors, clergy, teachers, farmers and workers.

After winning 9 seats in the 1952 parliamentary election, Bandaranaike contested the 1956 election on a platform of giving true meaning to the independence achieved in 1948. This involved a nationalist, democratic and socialist program which saw the SLFP achieve a huge victory at the 1956 elections and is seen by many observers as a social revolution resulting in the eclipse of the Westernised elite.

The achievements of S. W. R. D. Bandaranaike's term of office include the reverting of major defence facilities from British to local control, initiating a shift in Sri Lanka's foreign policy from the West to the Non-Aligned Movement and lowering the voting age from 21 to 18 years of age.

Working people, a core base of support for the party, also benefited through the setting up of an Employee's Provident Fund and the empowerment of peasants through the Paddy Lands Act. The healthcare and education systems were also improved for the benefit of the common man with the establishment of ayurvedic research centres, recognition of native physicians as well as the allowing of students to learn in their mother tongue (rather than only English).

The S. W. R. D. Bandaranaike government also had a lasting contribution in language policy. In 1956 Sinhala replaced English as the sole official language of Sri Lanka, fulfilling a major election pledge. In reaction to Tamil unease to this change, the Bandaranaike–Chelvanayakam Pact was signed to grant official status to the Tamil language as well. However, the agreement was vehemently opposed by hardline Sinhalese nationalists led by the UNP and instead a watered down act was passed. In September 1959, Bandaranaike was assassinated by Talduwe Somarama, an extremist Buddhist monk opposed to Bandaranaike's supposed attempts to appease the Tamils. He was replaced as prime minister for an interim period by Wijeyananda Dahanayake.