[4] Arizona State offensive coordinator Rob Likens had also shown interest in Slovis, but was unable to recruit him before he committed to the Trojans.

Slovis made his first collegiate appearance in the Trojans' season opener against the Fresno State Bulldogs, after Daniels suffered a season-ending knee injury.

[7][8] Slovis would go on to make his first start next week, where he set the school record for quarterback touchdowns in a 45–20 victory over the 23rd ranked Stanford Cardinal.

[29][30] On July 14, 2020, he was named to the Davey O'Brien Award Watch List alongside other notable quarterbacks, including 2020 Heisman Trophy favorites Trevor Lawrence and Justin Fields.

In September, Slovis sent an open letter alongside several other USC players convincing Governor of California Gavin Newsom to loosen restrictions related to the pandemic to possibly allow for a 2020 season.

[32][33] In week one of the 2020 season, against the Arizona State Sun Devils, Slovis set a USC record of 40 completions as he threw for 380 yards and 2 touchdowns in a 28–27 comeback victory.

[35] The following week, the Trojans traveled to Tucson to play the Arizona Wildcats, where Slovis led another 4th quarter comeback, throwing for 325 yards and 1 touchdown in the 34–30 victory.

[36] In Week 3, Slovis threw for 264 yards, 2 touchdowns and 1 interception en route to defeating the Utah Utes in Salt Lake City, for the first time since 2012, and improving USC's record to 3–0.

[37] Following the cancellation of their Week 4 matchup against the Colorado Buffaloes due to COVID-19,[38] Slovis led USC to a 38–13 victory over the Washington State Cougars, throwing for 287 yards and 5 touchdowns (4 of which were to Amon-Ra St.

[39] In the final week of the regular season, Slovis helped rally the Trojans from an 18-point deficit by throwing for 344 yards and 5 touchdowns (including the game winner to St. Brown with under a minute left) in a 43–38 victory over their crosstown rivals, the UCLA Bruins.

[46] The next week, he threw for 195 yards with a touchdown and an interception, before sustaining an injury that kept him in for the second-half, as the Panthers lost in overtime to the 24th ranked Tennessee Volunteers.

[47] He and backup quarterback Nick Patti missed the game against the Western Michigan Broncos due to injury, which saw third-string redshirt freshman Nate Yarnell start in their absence.

[51] The Panthers ended their regular season with wins over the Virginia Cavaliers, the Duke Blue Devils and Miami Hurricanes, which saw Slovis throwing five touchdowns as well as three interceptions.

[60] After a 35–6 loss to the Texas Longhorns,[61] Slovis was unable to start against the West Virginia Mountaineers, as he struggled with shoulder and elbow injuries to his throwing arm.

[62] Although named as an emergency quarterback against West Virginia,[63] the Texas game proved to be his final appearance for the Cougars, and Jake Retzlaff took over for the rest of the season.