Underwood will replace Travis Ford, who was officially let go last week.
“There’s not enough adjectives to describe how excited I am for the opportunity to coach where some of the greatest coaches in the history of college basketball have cut their teeth,” Underwood said in a statement.
Underwood, 52, was an assistant for Frank Martin at Kansas State and South Carolina before being hired at Stephen F. Austin three years ago. His record is 89-14 and is tied with Brad Stevens (Butler, 2008-10) for the most wins in the first three years of a coach’s tenure at an NCAA school.
Underwood took the Lumberjacks to the NCAA tournament in each of his three years. Stephen F. Austin upset Shaka Smart’s VCU team in Underwood’s first season at the helm. The Lumberjacks beat West Virginia in the first round last week before losing to Notre Dame on a last-second shot in the second round Sunday.
“I named three things that I was looking for in the new head basketball coach at Oklahoma State: character, coaching style and fit,” Oklahoma State athletic director Mike Holder said in a statement. “Brad Underwood gets the highest marks in each of those categories.”