"It's been a long process, thinking about this and that, the pros and cons of leaving college," said Beasley -- who said he will sign with an agent, making the decision irreversible. "I think it's time for me to take my game to the next level."
Beasley, a finalist for this season's Wooden and Naismith awards, made his decision public during a televised press conference.
The 6-foot-10 235-pounder was third in the nation in scoring, averaging 26.2 points per game, and also averaged 12.4 rebounds per contest -- second-best in the country.
Kansas State made its first NCAA Tournament appearance in 12 years this season, falling to Wisconsin in the second round.
A Washington native who attended four different high schools, Beasley was a McDonald's All-American during his senior year at Notre Dame Prep in Fitchburg, Mass.