Terms of the deals were not disclosed Saturday.
Harden, the third overall pick in the draft, was a first-team All-American and the Pac-10 player of the year after averaging 20.1 points, 5.6 rebounds and 4.2 assists during his sophomore season at Arizona State. He can earn about $4 million as a rookie.
Mullens was the sixth man of the year in the Big Ten. Ibaka spent this past season playing professionally with Ricoh Manresa of the Spanish ACB League.