O'Brien was sidelined last season as a medical redshirt after undergoing his second surgery on his left foot. He originally injured his foot during the 2010-11 season.
O'Brien averaged career highs of 13.8 points and 6.4 rebounds as a sophomore. He was the America East rookie of the year as a freshman.
Temple coach Fran Dunphy "is a great coach," said O'Brien, who visited Temple two weeks ago. "After meeting his staff and the players, I knew it was the right fit for me."