Originating from the town of Sukadana in West Kalimantan, he built a career as a businessman before entering politics, founding the Regional Unity Party and later joining Hanura, where he has served as chairman since December 2016.

Oesman, often nicknamed OSO, was born in the town of Sukadana in West Kalimantan province on 18 August 1950 to parents from other parts of Indonesia.

[2] He became a member of the People's Consultative Assembly (MPR) for the 1999–2004 period, and was appointed deputy speaker of the body on 11 August 2002.

[10] Following this, he founded the Regional Unity Party on 18 November 2002 and it participated in the 2004 elections, but only gathered 0.58 percent of votes and failed to secure seats in the People's Representative Council (DPR).

[11][12] He attempted to run as governor of West Kalimantan in the 2007 gubernatorial elections, but placed last out of three candidates behind winner Cornelis and incumbent Usman Ja'far.

[16] His appointment received criticism, since Oesman then held two major parliamentary positions in addition to being chairman in Hanura.

[22] Following the split, multiple members holding positions in the People's Representative Council were replaced with Hanura legislators in Oesman's faction.

[23] The other faction moved to support candidates not initially endorsed by the party in the 2018 regional elections, such as in East Java.