He was a standout three-sport athlete in football, basketball and track at Lincoln Northeast High School.
He made 68 tackles, 4.0 sacks, three passes defensed, two forced fumbles and one blocked punt as a senior.
Johnson (6 ft 4+3⁄8 in, 1.940 m; 259 lb, 117 kg) had a complete workout at combine, but he did everything again at the Pro Day.
Johnson was signed as free agent by the New Orleans Saints on November 29, 2006, and was inactive for one game.
Johnson joined the St. Louis Rams on February 5, 2007, on a waiver claim from the New Orleans Saints.