In his final season as a Colt, Mackey played in Super Bowl V on January 17, 1971. He was involved in a famous game-changing play where he caught a record-setting 75 yard pass from quarterback Johnny Unitas after the ball was deflected twice, once by fellow Colts player Eddie Hinton and once by opposing Dallas Cowboys defenseman Mel Renfro. Baltimore won the game 16–13, following a 32-yard field goal by Jim O'Brien with five seconds left.

A five-time Pro Bowler, Mackey was inducted into the Pro Football Hall of Fame in 1992, the 2nd pure tight end elected.

This Baltimore Colts mini helmet was signed in blue by Mackey and inscribed, "Balto Colts" and "NFL HOF 1992." This mini helmet includes a Great Moments COA.