Onstad served as Minority Leader from 2001 until his electoral defeat in 2016. Prior to that, he has been Assistant Minority Leader as well as alderman for Parshall City Council and officer for Booner Township. He is the owner/manager of a farm and also employed by Mountrail-Williams Electric Cooperative. Onstad's professional experience includes President of Parshall 2000 Incorporated; teaching in the Parshall School District from 1975 to 1983; being an owner/manager in farming since 1983; and working for Mountrail-Williams Electric Cooperative since 1998. He earned his BS in mathematics from Dickinson State University in 1975.
Onstad and his wife, Kathy, have three children; Sarah, Jaclyn, Andrew.