He played college football for the Alabama Crimson Tide and was selected by the Baltimore Ravens in the fourth round of the 2003 NFL draft.

Johnson grew up mostly in Cedar Key, Florida and attended Chiefland High School where he was a second-team all-state defensive end and tackle as a junior.

As a senior, he was a First-team SEC pick and Second-team All-American, he finished second in University of Alabama history with 23 sacks.

His 25 tackles for a loss tied Leroy Cook (1972–75) for second place on the school's career-record list behind Kindal Moorehead's record of 34 (1998–2002).

[3][4] In 2007 Johnson started all 16 games for the first time in his career and finished the season with a career-high 94 tackles (59 solo), despite being slowed for much of the year with a broken thumb.

But more importantly, Johnson's consistency and effort helped the Bolts rank ninth in the NFL in total defense and sixth against the run.

[9] In 2017 Johnson joined the Ravens' radio broadcast crew, to serve as a color analyst for four regular-season games.

Beginning with his great-grandfather, all of the men in the Johnson family worked on the water, including his father, Ludwig, who was lost at sea two weeks before Jarret's eighth birthday.