The FMLN was formed as an umbrella group on 10 October 1980, from five leftist guerrilla organizations; the Farabundo Martí Popular Liberation Forces (FPL), the People's Revolutionary Army (ERP), the National Resistance (RN), the Communist Party of El Salvador (PCES) and the Revolutionary Party of the Central American Workers (PRTC).

After the Chapultepec Peace Accords were signed in 1992, all armed FMLN units were demobilized and their organization became a legal left-wing political party in El Salvador.

In 1979, farmers went on strike for higher wages and better working conditions on Hacienda California, a large farm in Tierra Blanca.

Due to this strike, National Guard troops responded to the growing violence in Tierra Blanca using military force.

[16] On 17 December 1979, in a period of national crisis, the three dominant organizations (FPL, RN and PCS) of the Salvadoran left formed the Coordinadora Político-Militar (CPM).

The CPM's first manifesto was released on 10 January 1980, and the day after, the Coordinadora Revolucionaria de Masas was formed as a union of revolutionary mass organizations.

It is alleged by the United States that some credit for the unity of the five organizations that formed the FMLN may belong to Cuba's Fidel Castro, who facilitated negotiation between the groups in Havana in December 1979.

The Unified Revolutionary Directorate (Dirección Revolucionaria Unificada [es]) was created by the FPL, RN, ERP and PCS.

In December 1980, the Salvadoran branch of the Partido Revolucionario de los Trabajadores Centroamericanos broke away from its central organization and affiliated itself to FMLN.

Insurgents ranged from children to the elderly, both male and female, and most were trained in FMLN camps in the mountains and forests of El Salvador to learn military techniques.

In that offensive, the FMLN caught the Salvadoran government and military off guard by taking control of large sections of the country and entering the capital, San Salvador.

Soon after the November 1989 offensive, the U.S. government started to support negotiations to end the civil war, whereas up to that point they had pursued a policy of military defeat of the FMLN.

The death of the FMLN's long standing leader, Jorge Schafik, boosted Violeta Menjivar's political campaign which ultimately led her to narrow win in the election of San Salvador's mayor.

The FMLN's candidate in the 21 March 2004 presidential election, Schafik Hándal, won 35.6% of the vote, but was defeated by Antonio Saca of ARENA.

This was possible because one of the largest progressive coalitions in El Salvador called The Popular Social Bloc formed a pact with FMLN to help the political party win more seats in the Legislative Assembly.

The leaders of this split (including FMLN commandante Joaquin Villalobos of the ERP) then formed the Partido Democrata (Democratic Party), which was short-lived.

Out of this internal conflict, two organized tendencies emerged in the FMLN—the Renovadores ("Renovators" or "Renewal Movement") and the Corriente Revolucionario y Socialista (CRS—Revolutionary Socialist Current).

After the Renovadores vs Revolutionary Socialist Current factionalism, the FMLN's leadership decided to stop organized internal tendencies, and none have emerged since then.

[20] On 10 February 2016, the El Salvador Supreme Court ruled that Funes would face a civil trial for charges of illegally laundering more than $700,000 in personal bank accounts.

[28] FMLN was born through liberation theology priests who promoted the "conscientization" of the Salvadoran working class, who argued that their desperation and poverty was not "God's will or the result of their own failures" but rather the consequence of capitalism; the party would even earn the support of Archbishop Óscar Romero, who believed that oppressive conditions made some forms of violence acceptable, stating: "Christians are not afraid of combat; they know how to fight, but they prefer the language of peace.

The clergy was further radicalized after Romero was murdered by a right-wing death squad, with priests such as Rogelio Poncel fleeing to mountains and joining the Marxist-Leninist ERP guerillas there, which would later become one of the co-founders of the FMLN.

[29] The FMLN has a symbiotic relationship with the Catholic Church marked by mutual support, leading political scientists to compare the party to the similarly pro-Catholic Sandinista National Liberation Front of Nicaragua.

Through liberation theology, Salvadoran clergy would radicalize the local peasantry into joining and aiding the FMLN; in 1977, one Jesuit remarked: "Slowly the peasants began to abandon their fatalism, slowly they began to understand that their hunger, their disease, their infant mortality, their unemployment, their unpaid wages, were not the will of God but the result of the greed of a few Salvadorans and of their own passivism.

"[5] Being initially a mix of Marxism-Leninism and liberation theology,[30] the FMLN would moderate in the late 1980s and hold peace talks with the Salvadoran government, demanding power-sharing and transition to democratic rule.

The leaders of FMLN and FDR established alliances and agreements with social-democrats figures from Latin America, Canada and Europe, which caused their political mutation as the prospect of a negotiated settlement became more and more possible.