Chalmers, whose overtime-forcing three-point shot made him the hero of Kansas' NCAA championship game in April, had announced his intention to enter the draft but hadn't hired an agent. That kept the option to return to Kansas open.
But Kansas Coach Bill Self said he was informed Sunday that Chalmers wouldn't.
"We are excited for Mario's draft prospects," Self said. "From what we have gathered his stock has climbed. We wish Mario the very best and we will anxiously be waiting to see where all of our other guys will be drafted."
Chalmers was Kansas' second-leading scorer last season at 12.8 points a game. His three-point shot with 2.1 seconds left in regulation of the national title game forced overtime and allowed the Jayhawks to defeat Memphis 75-68.