Wainwright spent 4 ½ seasons at DePaul and compiled a 59-80 overall and 20-51 Big East record before being fired by the Blue Demons on Jan. 11, 2010.
“We are very grateful to add coach Wainwright as the final member of our staff,” Marquette coach Buzz Williams said in a statement. “I have known coach since early in my career and have always been humbled by his willingness to share wisdom with me as I have advanced.
“I never knew as we were building our relationship, that an opportunity like this would ever materialize, but I am very grateful that it has. His wealth of knowledge and experiences will help everyone in our program on one level or another.”
Wainwright spent the 2011-12 season as Fresno State's associate head coach.
Wainwright is originally from Berwyn, Ill. and coached early in his career at East Leyden High School and Highland Park High School in the Chicago suburbs.