[3][4] In his senior season, Mobley averaged 20.5 points, 12.2 rebounds, 5.2 blocks, and 4.6 assists per game, leading Rancho Christian to a 22–8 record.

He repeated as California Gatorade Player of the Year, joining Jrue Holiday as the award's only two-time winners.

[8] On August 5, 2019, he committed to play college basketball for USC over offers from UCLA and Washington, among other major NCAA Division I programs.

Sources: In his college debut for USC on November 25, 2020, Mobley scored 21 points and had nine rebounds in a 95–87 overtime win against California Baptist.

[10] On March 11, 2021, at the Pac-12 tournament quarterfinals, he posted a career-high 26 points, nine rebounds and five blocks in a 91–85 double overtime victory over Utah.

[18] On August 8, 2021, Mobley made his summer league debut in a 84–76 loss against the Houston Rockets where he posted 12 points, five rebounds, and three blocks in 28 minutes.

[19] On October 20, he made his NBA debut, putting up 17 points, nine rebounds, and six assists in a 132–121 loss to the Memphis Grizzlies.

[22] On December 8, Mobley became the first Cleveland rookie since LeBron James in March 2004 to record five blocks in an NBA game.

[25] On January 21, 2023, Mobley scored a then career-high 38 points on 19-of-27 shooting from the field, along with nine rebounds and three assists in a 114–102 win over the Milwaukee Bucks.

[27] On May 9, Mobley was named to the NBA All-Defensive First Team[28] On November 28, 2023, Mobley recorded 17 points, 19 rebounds, and 7 blocks in a 128–105 win over the Atlanta Hawks during the team's final In-Season Tournament matchup, setting a season-high in blocks and a career-high in rebounds.

He became the second NBA player under the age of 25 (after Kevin Durant) to record 40+ points, 10+ rebounds, 3+ blocks, and 5+ three-pointers made in a game.

[36][37] Mobley joined the United States for the 2019 FIBA Under-19 World Cup in Heraklion, Greece, but he was limited to playing two games and a total of seven minutes in the tournament due to back spasms.