Thomas averaged 19.8 points and 5.9 rebounds per game this season, led the team to the regional finals in the NCAA Tournament where they lost to Wichita State, and was named a third-time All-American selection.
Thomas finishes his career with 1,630 points, which ranks ninth in school history.
Thomas has been projected to be drafted in the late first round or early second.
"My three years at Ohio State have been the best years of my life,” Thomas said in a statement. “I have grown tremendously as an individual and as a basketball player. I intend to return to finish my degree, but I believe that now is the best opportunity to pursue my dream and begin my career as a professional basketball player. I will always be a Buckeye and am blessed to be a part of the Ohio State University family."