[2] In course of the Second Sudanese Civil War, he served as administrator of the refugee camp of Itang, as head of the SPLA's relief wing in Nasir,[5] and as Machar's quartermaster.

[6] When Machar's loyalists split from the SPLA (Mainstream) and formed the SPLA-Nasir,[5] Deng acted as the main intermediary between the latter and the Sudanese government.

Deng was consequently elected governor of Unity State, resulting in tensions between Machar and another local pro-government militia leader, Paulino Matip Nhial, which escalated in violence from 1998 to 1999.

[2] When the South Sudanese Civil War broke out, Deng initially joined the SPLM-IO rebels of Riek Machar, and became the latter's second-in-command.

They subsequently began to fight alongside the government force against Machar's loyalists,[12][13] resulting in Deng being regarded as "traitor" by other rebels.

[15] In January 2020, The U.S. Treasury Department sanctioned Deng "for his involvement in serious human rights abuse, including the disappearance and deaths of civilians.