After graduating from Chicago's Westinghouse High School, Johnson, a sharpshooting 6'7" forward/guard, attended the University of Illinois, majoring in history, before being selected by the Kansas City Kings in the 1981 NBA draft.

Johnson would play for the Kings, the Phoenix Suns, the Seattle SuperSonics, the Charlotte Hornets, the Indiana Pacers, the Houston Rockets, and Greek team Olympiacos (1994–1995) before retiring from basketball in 1999.

Johnson's career point total of 19,202 is also higher than all but 30 inductees into the Naismith Memorial Basketball Hall of Fame.

Johnson also played for one year in the Greek Basket League, with the FIBA EuroLeague powerhouse Olympiacos Piraeus, in the 1994–95 season.

Along with his Sixth Man of the Year Award, he is also remembered for hitting the game-winning three-pointer as time expired in a 95–92 Rockets win over the Utah Jazz in game 4 of the 1997 Western Conference Finals.

Johnson called that day the "worst...of his life" and expressed concern that the case of mistaken identity might permanently sully his reputation.