From 2018 to 2020 at Tennessee, Tillman was a backup receiver and had eight receptions for 124 yards and two touchdowns.[5][6] He redshirted as a freshman in 2018.[7] He scored his first college touchdown on September 14, 2019, in the 45–0 victory over Chattanooga.[8] In the final game of Tennessee's 2020 season, he scored on a 46-yard touchdown reception in a 34–13 loss to Texas A&M.[9]
Tillman became a starter for the first time in 2021.[10] Tillman had his breakout game against longtime rival #4 Alabama with seven catches for 152 receiving yards and a receiving touchdown in the 52–24 loss.[11] His touchdown was a 70-yard reception that helped put the Vols within seven points in the fourth quarter.[12] On November 13, against rival #1 Georgia, he had ten receptions for 200 receiving yards and one touchdown in the 41–17 loss.[13] Tillman was the first Volunteer to record at least 200 receiving yards since Cordarrelle Patterson in 2012.[14] In the regular season finale against in-state rivalVanderbilt, he had his first multi-touchdown game as a Vol in the 45–21 victory.[15] Tennessee earned a spot in the Music City Bowl against Purdue. In the 48–45 overtime loss, he had seven receptions for 150 receiving yards and three receiving touchdowns.[16] He finished the season with 64 receptions for 1,081 yards and 12 touchdowns.[17][18] His 12 touchdowns ranked third in the SEC.[19]
Tillman returned to Tennessee in 2022, rather than enter the 2022 NFL draft.[20][21] In Tennessee's second game, against #17 Pitt, he had nine receptions for 162 yards and the go-ahead touchdown in overtime in the 34–27 victory on September 10.[22] Tillman suffered an ankle injury in the following game against Akron that impacted his availability and production for the remainder of the season.[23] Tillman returned against Kentucky on October 29.[24] On November 19, he scored two receiving touchdowns against South Carolina.[25] He finished the season with 37 receptions for 417 receiving yards and three receiving touchdowns in six games.[26] He elected to enter the 2023 NFL draft and not participate in the Orange Bowl.[27]
Tillman was drafted by the Cleveland Browns in the third round, 74th overall, of the 2023 NFL draft.[30] In his rookie season, Tillman appeared in 14 games and started three. He finished with 21 receptions for 224 receiving yards.[31]
In Week 8 of the 2024 season, Tillman recorded 99 yards and his first two professional touchdowns against the Baltimore Ravens in a 29–24 victory.[32] After suffering a concussion and leaving the game in the Week 12 matchup against the Pittsburgh Steelers, Tillman was ruled out for the team's Week 13 matchup against Denver Broncos.[33] Tillman was placed on injured reserve due to the concussion on December 31, ending his season with 29 receptions for 339 yards and three touchdowns.[34]