Born in Detmold, Lippe-Detmold,[1] Küstermann graduated from high school and worked at a store in Hamburg, Germany before immigrating to the United States when he was 18.

[1][2] Kustermann worked at a St. Louis, Missouri hardware store for several months before moving to Green Bay, Wisconsin.

He served on the board of directors of the Citizens National Bank, and was an officer of the Green Bay Businessmen's Association.

[4] He was twice an unsuccessful candidate for Congress, and served as Postmaster of Green Bay during the administration of Benjamin Harrison.

He died in Green Bay on December 25, 1919[1] and is buried in Allouez, Wisconsin's Woodlawn Cemetery.