Slovis entered the 2019 season as the second quarterback in the depth chart, behind then-starting quarterback JT Daniels. Slovis made his first collegiate appearance in the Trojans' season opener against Fresno State, after Daniels suffered a season-ending knee injury. 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. For his efforts, Slovis was named the PAC-12 Freshman of the Week. The next week, Slovis started in an away game against BYU, where he would throw three interceptions in a 30–27 loss in overtime. Slovis would next start in a home game against the 10th ranked Utah Utes, where he left the game early in the first quarter after suffering a possible head injury. Backup quarterback Matt Fink would proceed to lead the Trojans to a 30–23 upset victory. Following the incident, Slovis was placed in the concussion protocol and ruled out for the next game, an away game at Washington, leaving Fink to start. Slovis would return to the starting position for the next game, a narrow loss at 9th ranked Notre Dame. Rebounding from that loss, Slovis would lead the Trojans to two straight wins, a blowout against Arizona and a come from behind victory in USC's first away game win of the season at Colorado. For his performance in the Colorado victory, Slovis was awarded his second PAC-12 Freshman of the Week Award. Following a 56–24 blowout loss to Oregon, where Slovis set the USC record for most pass attempts in a game, Slovis would return to his native Arizona where he set another school record with 292 passing yards and 4 touchdowns in the first quarter of a 31–26 victory against Arizona State. For his performance, Slovis was awarded the PAC-12 Player of the Week Award, while freshman Kenan Christon was named the PAC-12 Freshman of the Week. The following week, Slovis led the Trojans to a 41–17 blowout of Cal going 29/35 for 406 yards, 4 touchdowns and zero interceptions. In the final game of the regular season, Slovis broke another USC record throwing for single game passing yards, throwing for 515 yards and 4 touchdowns in a 52–35 win over UCLA. It was his fourth game of at least 400 yards passing, setting yet another school record. During the 2019 Holiday Bowl, with USC down 28–24 but making a comeback, Slovis suffered an elbow strain in the second quarter after getting sacked by A. J. Epenesa. He was replaced by Matt Fink and USC would lose to the Iowa Hawkeyes 49–24. Slovis finished the 2019 season with a freshman record 3,502 yards, 30 touchdowns to only 9 interceptions and an NCAA Freshman record 71.8 completion percentage, while leading USC to an 8-4 regular season record and a Holiday Bowl berth en route to being named the PAC-12 Freshman of the Year.
Sophomore season
Following the 2019 season, multiple sources pegged Slovis as a possible contender for the Heisman Trophy in 2020. 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.
