Sears announced his decision earlier Tuesday via Twitter.
"The past week has been a difficult time, a bump in the road, and it makes me realize that life is not linear," he wrote. "I love my teammates, football, USC, and the USC degree. Nobody can ever take that degree away from me."
Sears' decision came less than one week after coach Clay Helton announced sophomore JT Daniels would start for the second straight season. The Trojans held an open audition among all four scholarship quarterbacks during spring practice and preseason camp as part of their transition to the Air Raid spread offense. Freshman Kedon Slovis was named the backup, with redshirt junior Matt Fink third on the depth chart and Sears fourth, leading to the expectation that Sears would seek other options.
Sears plans to remain at USC for the fall semester to complete his undergraduate degree in December, which would allow him to talk to other schools and coaching staffs and be immediately eligible to play next season without having to sit out.
"We do a great job of getting our students graduated within three, three-and-a-half years," Helton told ESPN's Edward Aschoff on Tuesday. "Jack has used every resource in order to get that done, so congratulations to him."
Helton said Sears had the option of remaining with the team while in the portal, but chose to leave the team entirely, despite writing in his statement that he informed Helton he would be available if needed.
"He thought right now for himself that it was best for him to focus on his studies, focus on being able to visit with other [schools], and he's done everything for us," Helton said. "I don't hold it against him at all. He's competed here, he's given his absolute best effort at all times, he's been a great teammate, and now he's going to be a graduate of this university, and that gives him the honor of going to play [at another school] if he chooses to."
Sears, who replaced former Trojans starter Sam Darnold at San Clemente High in Southern California, started once for USC last season due to injuries to Daniels and Fink. He completed 20 of 28 passes for 235 yards with a pair of touchdowns in a loss to Arizona State.
He arrived at USC as the No. 5-ranked pocket passer in the Class of 2017 and was ranked No. 103 overall in the ESPN 300.
Helton also said that freshman defensive back Jayden Williams' transfer waiver has been approved and he's eligible to play against Fresno State on Saturday.
The USC coach also said that five-star freshman wide receiver Bru McCoy's waiver status for immediate eligibility is still being processed by the NCAA and he is unlikely to be available before Saturday. The former No. 1-ranked athlete prospect in the 2019 recruiting class transferred to Texas after committing to and enrolling at USC in January. He then transferred back to USC after spring ball with the Longhorns.
"The waiver has a lot of details with it," Helton told Aschoff. "This is not a common occurrence when you go from university to the next and back [to the original school]. There's a lot of things that go into it and we're taking our time with it."
Information from The Associated Press was used in this report.