In 1958, Onoh was elected member, House of Representatives for Enugu Constituency. He later resigned to take up appointment as the first indigenous chairman of the Board of the Nigerian Coal Corporation. From 1961 to 1966 he was on the board of the Nigeria Railway Corporation. During the civil war, Onoh was appointed administrator of Enugu Capital Territory. In 1970 he returned to private life as a lumber merchant. He was a founding member of Club 13, which evolved into the Nigerian People's Party (NPP), but later moved to the National Party of Nigeria (NPN). He fought unsuccessfully for the Anambra State governorship on the NPN platform in 1979. He was then appointed chairman of the Nigeria Mining Corporation, and in 1982, chairman of the Associated Ore Mines.
