Leonard is skipping his final two seasons after helping the Aztecs go 34-3 and reach the NCAA round of 16 for the first time. The Aztecs lost to eventual national champion Connecticut in the West regional semifinal.
Coach Steve Fisher met with Leonard and his family after the Final Four.
"We talked about where we thought I would be selected in the draft," Leonard said in a statement. "Coach Fisher gave me great advice and helped me with my decision that I should move forward with the process. This is very exciting. I have been preparing my whole life to play in the NBA and now I will have that chance."
Leonard, from Riverside, led the Aztecs with 15.5 points and 10.6 rebounds per game.
"Kawhi handled this season in as fine of fashion as a player can handle it," Fisher said in a statement. "After the Final Four, I met with Kawhi and his family and I presented everything in terms of the information I had. They were extremely receptive and at the end of the conversation we reached a decision that he would submit his name for the draft. I am totally supportive of Kawhi, his family and his decision."
Leonard has been projected by some to go in the middle of the first round. Michael Cage is the only SDSU player to be selected in the first round, going 14th overall to the Los Angeles Clippers in 1984.
"Kawhi is going to be an exceptional NBA player," Fisher said. "He will always be a San Diego State Aztec. The feeling he has for this university and program and the feeling our fans and community have for him will allow him to be welcomed back with open arms for years to come."
Leonard averaged 14.1 points and 10.2 rebounds in two seasons. He scored 990 points, which is the 19th-highest total in SDSU's Division I history, and had 716 rebounds, seventh all-time at SDSU and fifth in the program's D-I history.
He had 23 double-doubles in 2010-11, and 40 in 70 career games, including 69 starts.
"The last two years have been great," Leonard said. "I have been part of two conference tournament championships, a regular-season championship and two NCAA tournament teams. The whole community has been behind us and the student body has been so supportive. This has been a great experience and has set the stage for what is next."
The draft is June 23.