Tomey's Wildcats finished 5-6 this year and 3-5 for a fifth-place tie in the Pacific-10 Conference standings. Had the Cats beaten ASU they would have qualified for a bowl game.
"I had no other choice. I appreciate the opportunity I was given to coach at the University and to coach some tremendous Wildcats over the years.
Arizona athletics director Jim Livengood was not immediately available for comment. Tomey declined to elaborate on his decision.