Johnson began his collegiate career at Davidson College. He played in all 22 of the Wildcats' games with 19 starts over two seasons and was named first team All-Pioneer Football League as a sophomore. Johnson transferred to Boston College following his sophomore year.[1] Johnson said "Boston College for me was a no-brainer" and that he chose it because the school was renowned academically.[3]
Johnson started seven games at left guard in his first season at Boston College and was named second team All-Atlantic Coast Conference (ACC) after he was named the conference Offensive Lineman of the Week three times.[4] He was moved to left tackle before his senior season and was named third team All-ACC after starting all 11 of the Eagles' games.[5] After considering entering the 2021 NFL Draft, Johnson decided to utilize the extra year of eligibility granted to college athletes who played in the 2020 season due to the coronavirus pandemic and return to Boston College for a fifth season[6] He moved back to the guard position for his final season and was named first team All-ACC and a first team All-American by the Walter Camp Football Foundation.[7]
Johnson was selected in the first round with the 17th overall pick by the Los Angeles Chargers in the 2022 NFL draft.[10] He was named the Chargers starting right guard as a rookie, starting all 17 games. He was named to the PFWA All-Rookie Team.[11] In his second season, he was moved to left guard, his natural position in college.[12]