During the ensuing war of independence, FRELIMO received supported from China, the USSR, the Scandanavian countries, and some non-governmental organisations in the West. Its initial military operations were in the North of the country; by the late 1960s it had established "liberated zones" in Northern Mozambique in which it rather than the Portuguese constituted the civil authority. In administering these zones it was necessary for FRELIMO to tangibly improve the lot of the peasantry in order to receive their support. It freed them from subjegation to landlords and Portuguese-appointed "chiefs", and established cooperative forms of agriculture. It also greatly increased peasant access to education and health-care -- the latter often administered by FRELIMO soldiers assigned to medical assistance projects. Its practical experience in the liberated zones lead FRELIMO increasingly toward a Marxist policy. FRELIMO came to regard economic exploitation by Western capital as the principal enemy of the common Mozambican people, not the Portuguese as such, and not Whites. Thus, although an African nationalist party, it adopted a non-racial stance, and in fact included a number of Whites and mulattoes among its members.
The early years of the party, during which its Marxist direction evolved, were the occasion of some internal turmoil. The line described above: that is, to fight not merely for independence but also for a change to a socialist society, was championed by Mondlane, along with dos Santos, Machel, Chissano and a majority of the Party's Central Committee. The socialist position was approved by the Second Party Congress, held in July 1968. Mondlane was reelected party President and Uria Simango was re-elected vice-president.
In 1969, Eduardo Mondlane was murdered by a bomb. After the discovery of Gladio's secret "stay-behind" NATO armies in the 1990s, it was discovered that Aginter Press, Portugal's branch of Gladio, had been directly involved in the assassination of FRELIMO's leader.
After Mondlane's assassination, Uria Simango took over the leadership, but his presidency was disputed. In April 1969, leadership was assumed by a triumvirate comprising Samora Machel, Marcelino dos Santos and Uria Simango. Simango was ousted in November 1969 and left FRELIMO to join another small liberation movement COREMO (Revolutionary Committee of Mozambique).
FRELIMO controlled most of the northern region of the country by 1964. By the early 1970s, FRELIMO's 7,000-strong guerilla force had wrested control of much of the central and northern parts of the country from the Portuguese authorities and was engaging a Portuguese force of approximately 60,000 men. In 1975, after the April 1974 Carnation Revolution, Portugal and FRELIMO negotiated Mozambique's independence, which came into effect in June of that year. FRELIMO then established a one-party state based on Marxist principles with Samora Machel as President. The new government received diplomatic and some military support from Cuba and the Soviet Union. Marcelino dos Santos became his vice-president while Uria Simango, his wife Celina and other prominent Frelimo dissidents including Paulo Gumane and Adelino Gwambe (former leaders of UDENAMO), were arrested and extra-judicially executed.
After Machel's death in 1986, in a suspicious airplane crash, Joaquim Chissano began to lead both the party and the state. Despite his education in the Communist bloc countries, Chissano was not a hard-line Marxist and called for democratic, multi-party elections in 1994 that put an end to single-party rule.
The party thus selected Armando Guebuza as its candidate in the presidential election on December 1-2 2004 where he won expectedly with about 60% of the vote. At the last legislative elections of the same date the party won 62.0 % of the popular vote and 160 out of 250 seats. RENAMO and some other opposition parties made claims of election fraud and denounced the result. These claims were supported by international observers (among others by the European Union Election Observation Mission to Mozambique and the Carter Center) to the elections who criticized the fact that the National Electoral Commission (CNE) did not conduct fair and transparent elections. They listed a whole range of shortcomings by the electoral authorities that benefited the ruling party FRELIMO. However, the elections shortcomings have probably not (also according to EU observers) affected the final result in the presidential election. The distribution of parliamentary seats among the parties will have been somewhat altered though, RENAMO probably losing some seats to FRELIMO. The Shangaan ethnic group is noted for its support for FRELIMO.
Mozambique's national anthem from 1975 to 1992 was Viva, Viva a FRELIMO ("Long Live FRELIMO").