Coming out of Mater Dei High School in Santa Ana, California, Amon-Ra St Brown was a five-star prospect according to 247 Sports and Rivals. Prior to his commitment to USC, St Brown had offers from Florida, Alabama, and Notre Dame.
As a freshman in 2018, St Brown started in five games, but appeared in all twelve for USC. He finished with 750 receiving yards on 60 receptions, along with three touchdowns.
In 2019, St Brown saw an increased role in the USC offense, which resulted in 77 catches on 1,042 yards. Additionally, he finished with six touchdowns. Further, he finished with at least 100 receiving yards on four occasions. Following the 2019 season, Amon-Ra St Brown underwent surgery for a sports hernia.
The 2020 season was shortened due to the coronavirus, but Amon-Ra St Brown was still able to finish with 41 receptions for 478 yards and seven touchdowns. Furthermore, St Brown had two games with more than 100-yards receiving in each.