Martin, 46, is the 32nd men's basketball coach at South Carolina, the school announced Tuesday.
Martin, who had three seasons remaining on his Kansas State contract, reportedly agreed to a six-year, $11.9 million deal with South Carolina. He was being paid about $1.2 million a season at Kansas State.
He replaces Darrin Horn, who was fired two weeks ago after South Carolina completed a 10-21 season (2-14 in the Southeastern Conference). In four seasons under Horn, the Gamecocks were 60-63, with a 23-41 mark in the SEC.
Martin took over at Kansas State in 2007 after Bob Huggins, who was in Manhattan, Kan., for one season, left the Wildcats to coach West Virginia. Ironically, West Virginia will play Kansas State in the Big 12 Conference next season.
The Kansas State position was Martin's first collegiate head coaching job. The Wildcats were 117-54, with a 50-32 Big 12 record, with Martin as coach. Kansas State went to the NCAA Tournament each season under Martin except his second, when the Wildcats took a National Invitation Tournament berth.