Kustermann worked at a St. Louis, Missouri hardware store for several months before moving to Green Bay, Wisconsin. He worked as the bookkeeper for the Green Bay Advocate newspaper, and later owned and operated his own store dealing in musical instruments, stationery and other items. He served on the board of directors of the Citizens National Bank, and was an officer of the Green Bay Businessmen's Association.[3]
A Republican, Kustermann served on the Green Bay City Council and as the City Treasurer. He later served on the Brown County Board of Supervisors, and was a member and President of the state Board of Control.[4] He was twice an unsuccessful candidate for Congress, and served as Postmaster of Green Bay during the administration of Benjamin Harrison.[5]