Johnson has appeared in 103 career regular season games (88 starts) during his seven-year NFL career with the Rams (2017-20, 2023) and the Cleveland Browns (2021-22). He has recorded 540 tackles (361 solo), 13 tackles for loss, 14 interceptions with 190 return yards, 47 passes defended, 31 pass breakups, four forced fumbles, two fumble recoveries, 1.0 sack, 11 pressures, five quarterback hits and five hurries. Johnson also has seen action in seven postseason contests (all starts) with the Rams and notched 42 tackles (31 solo), one interception, three passes defended and two pass breakups. He was selected by the Rams in the third round (91^st overall) of the 2017 NFL Draft.

Johnson played collegiately at Boston College, where he saw action in 45 games (27 starts) and totaled 167 tackles (122 solo), six interceptions for 47 return yards, 14 passes defended, 12 pass breakups, 3.5 tackles for loss, three forced fumbles, two fumble recoveries, and 1.0 sack. His senior year in 2016, he served as a team captain, led the team with three interceptions, tied for third in the ACC in interception return yards, and ranked ninth in the conference with nearly one pass breakup per game.