Baxter coached last season at Michigan.
“We are very excited to welcome back John Baxter to our Trojan family,” Helton said in a statement. “He is one of the most respected coaches in our profession at any position. His units have been near the top of the collegiate special team efficiency rankings almost every year. Having worked alongside him in the past, I know Coach Baxter as one of the best teachers and skill developers in football today. We look forward to our special teams rising to greater heights under him.”
Baxter, 52, was a longtime assistant at Fresno State when former Trojans coach Lane Kiffin hired him at USC before the 2010 season.
Steve Sarkisian did not retain Baxter after Sarkisian was hired as coach before the 2014 season.
Johnny Nansen coached USC running backs and special teams the last two seasons.
Helton hired his younger brother, Tyson Helton, as running backs coach and passing-game coordinator, so Nansen’s role is still to be determined.
Helton also has hired Neil Callaway as offensive line coach and promoted receivers coach Tee Martin to offensive coordinator.
Helton has said he would have all or most of his staff in place by mid-January in anticipation of the final recruiting push toward national signing day in February.