Purnell, a 1975 graduate and former player at Old Dominion and an ex-Maryland assistant, beat out three other candidates who interviewed for the position that became available when former coach Tom Young was fired at the end of the season.
The Old Dominion job was one of two vacant coaching positions in which Truax had expressed interest. Truax, who has led the Tigers to consecutive National Collegiate Athletic Association tournaments, also said he plans to speak to Virginia Tech about its opening.
Other candidates at the Norfolk, Va., school reportedly were Bucknell coach Charlie Woollum, Charlotte Hornets scouting director Dave Twardzik and Norfolk high school coach Jack Baker.
Truax expressed his interest in the Old Dominion job just days after Towson was eliminated by Ohio State in the first round of the NCAA tournament. He initially contacted the school on March 19, and was called on Sunday for an interview.