Born in Racine, Wisconsin, to Robert Wittke, Sr. and Margaret Wittke, née Jankowski, Wittke graduated from William Horlick High School with a BA in 1975. He received his Ph.D. in Accounting from the University of Wisconsin-Eau Claire in 1980. From 1980 to 1986 he worked as an accountant at Modine Manufacturing in Racine and then at Snap-on Inc. in Kenosha from 1988 to 1994. From 1994 to 2002, he worked as a tax advisor at Deloitte. Since 2012, he has been with CORPTAX, a Deerfield, IL-based tax software-as-a-service company.
Wittke lives in Wind Point, Wisconsin and is married with four children.