"The Steelers drafted guys who were bigger, stronger and faster than I, but they never found one who could take my job away from me." - Jack Lambert

The Steelers took a chance on Lambert, and he rewarded them quickly when he replaced middle linebacker Henry Davis. Lambert went on to earn the NFL Defensive Rookie of the Year Award as a central figure on a great Steeler defense that went on to win their first Super Bowl by beating the Minnesota Vikings 16-6 in Super Bowl IX.

Jack Lambert played with maniacal intensity. He flew into tackles running at one hundred percent full speed. With no regard for his own safety,he took grim pleasure in inflicting maximum punishment on the opposition. A snarling Lambert intimidated the Dallas Cowboys in Superbowl X by slamming star safety Cliff Harris to the ground. By the time of his retirement, he was universally feared and recognized as one of the greatest linebackers in the history of the game. He was the Steelers starting middle linebacker, for eleven seasons; and according to Steelers media guides averaged 146 tackles per season through his 10th year. He recorded only 19 in his 11th and final season because of the injury suffered to his toe.

Jack Lambert amassed 28 career interceptions, 1,479 career tackles (1,045 solo), and (officially) 23½ sacks, although the unofficial sack total is greater since sacks did not become an official NFL statistic until 1982, Lambert's ninth year in the league. One of his official sacks, however, came in the 1983 season opener against the Denver Broncos, handing rookie quarterback & fellow Hall of Famer John Elway his first of what would be an NFL-record 559 career sacks Elway would absorb in his 16-year career.

Lambert's four front upper teeth were missing as a result of taking an elbow in basketball during high school. Although he had a removable partial denture he wore in public, he didn't wear it during games, and pictures of Lambert's toothless snarl became a signature of the famous Steeler defense and led to his being referred to as "Count Dracula in Cleats."

In 1976, Lambert assumed the role as leader of the Steelers after star defensive tackle "Mean Joe" Greene missed several games due to a chronic back injury. The Steelers 1976 defense is considered one of the greatest defenses of all time, finishing #1 in nearly every statistical category. After quarterback Terry Bradshaw, Lynn Swann and several other starters went down with injuries, the Steelers struggled to a 1-4 record. At a "players only" meeting, Lambert made it clear that "the only way we are going to the playoffs to defend our title is to win them all from here out, and threatening physical harm to anybody who didn't put forth the effort to do so." In a remarkable nine-game span, the Steelers defense allowed only two touchdowns and a total of 28 points, including 5 shutouts. The Steelers won all of these games and finished at 10-4. The defense gave up only 138 points for the entire season. Eight of the eleven defensive starters on the Steelers made the Pro Bowl that year. Jack Lambert was named NFL Defensive Player of the Year in 1976.

In a nine-year span, Jack Lambert was named to nine straight Pro Bowls and was NFL Defensive Player of the Year once. In 1984 a severe and recurring case of turf toe sidelined him, after which he retired. Presently he and his wife Lisa live in West Franklin Township, Pennsylvania, with their children (Lauren, Elizabeth, John and Ty.)

He has been a volunteer deputy wildlife officer and he now focuses on coaching youth baseball and basketball, tending to his land and maintaining his town's ball fields

In 2004, the Fox Sports Net series The Sports List named Lambert as the toughest football player of all time.

While Lambert's number 58 is one of many jersey numbers "unofficially retired" by the team (the Steelers do not retire jersey numbers), his jersey number has perhaps gotten the biggest attention out of all such jersey numbers. When Lambert retired, he reportedly told the equipment manager that he was to never issue number 58 again (being aware of the team's policy not to retire numbers).