He played football and wrestled at St. Joseph High School in Westchester, Illinois, where he was a three-year starter as a defensive tackle and offensive lineman and was named first-team All-area.
However, in the middle of his junior year, due to a coaching change and a losing season, Johnson transferred to Montini Catholic High School for his senior season, and in his only campaign at Montini, Johnson was named team captain and earned first-team All-state, All-conference and All-area honors as well as prep All-America recognition after helping the Broncos post 12-2 a record while winning the state championship, finishing with a 70–45 victory over Joliet Catholic.
It was Iowa coach Kirk Ferentz who convinced him to play for the Hawkeyes after he sent a personal letter that made an impression on Johnson.
Shortly after Signing Day, Johnson decommitted to take a closer look at Michigan State one more time, but ended up committing back to Iowa.
[1] Johnson had to wait a while before getting significant playing time due to Iowa's depth in the interior defensive line.
[4] According to Pro Football Focus (PFF), Johnson ranked sixth among defensive tackles in pass rush productivity with 43 combined pressures in 330 snaps.
In 2020, Johnson moved into a starting role after projected starter Michael Pierce opted out of the season due to concerns over COVID-19.
[13] On September 15, 2021, Johnson was signed by the Texans off the Saints practice squad after defensive lineman Vincent Taylor suffered an ankle injury.