General David Yau Yau has dissolved his party, the South Sudan Democratic Movement-Cobra Faction and joined the SPLM.
The military wing of the party fought the government for three years until they signed a peace agreement in 2014.
General Yau Yau announced the dissolution of his party at the SPLM secretariat in Juba this afternoon.
He spoke to journalists at a press conference attended by about 10 of his military commanders and traditional leaders.