Seto, who turned down the opportunity to become the defensive coordinator at Washington just weeks ago, will replace Nick Holt as USC's new defensive coordinator.
Holt left to join Steve Sarkisian at Washington, and was formally introduced as the Huskies defensive coordinator at a press conference on Tuesday.
Seto has spent 10 years on the USC coaching staff, including six as a full-time assistant.
The 32-year-old assistant was a walk-on linebacker for the Trojans in 1997 and has been a part of the football program in some capacity ever since.
He joined the coaching staff as a volunteer assistant in 1999 and has served as the secondary coach since 2006.
Pete Carroll also announced on Wednesday that Jethro Franklin will join the USC staff as the defensive line coach and linebacker coach Ken Norton Jr. is adding the title of assistant head coach for the defense.
Franklin, 43, served as the defensive line coach at USC in 2005, and has spent the past three seasons in the NFL, as a defensive line coach with the Tampa Buccaneers (2006) and Houston Texans (2007-08).
USC's new defensive coordinator Rocky Seto and Pete Carroll.
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