It was initially founded as the political wing of the Sudan People's Liberation Army (SPLA; a key belligerent of the Second Sudanese Civil War) in 1983.

The SPLM was formed as a Marxist-Leninist,[10] socialist,[11] rebel movement on 16 May 1983, after the Government of Sudan's abandonment of the Addis Ababa Agreement signed between the government of Gaafar Nimeiry and the Anyanya leader Joseph Lagu, who had first introduced the southern Sudanese to the effective political, economic, social, educational, and religious situations they would face after Sudan's independence.

[14] It fought against the governments of Gaafar Nimeiry, Sadiq al-Mahdi and Omar Hasan Ahmad al-Bashir in what is now called the Second Sudanese Civil War.

The war has been largely described in religious and ethnic terms, and also as a struggle for control of the water and oil resources located in southern and western Sudan.

The attempt failed but led to widespread fighting in the south and the formation of other rebel groups, such as Kerubino Kuanyin Bol's SPLA Bahr-al-Ghazal faction.

Several smaller factions signed the Khartoum Peace Agreement with the government in April 1997 and formed the United Democratic Salvation Front (UDSF).