In the 1979–1980 college season, King was named the ACC Men's Basketball Player of the Year. He appeared on the cover of Sports Illustrated twice during the 1980 season. One of the highlights of his ACC career was a thundering dunk over Duke center Mike Gminski during a Maryland home game at Cole Field House. Duke was No. 1 in the nation at the time, and King went on to lead the Terps in scoring that night and help topple the Blue Devils in the process. His jersey #55 was retired by the Maryland basketball program. In 2002, King was named to the ACC 50th Anniversary men's basketball team as one of the fifty greatest players in Atlantic Coast Conference history.
King played in nine NBA seasons for four different teams. He played for the Nets, Philadelphia 76ers, San Antonio Spurs and Washington Bullets. King's best years as a professional came during his playing days with the Nets from 1981–1987. During the 1982–83 season, he appeared in 79 games and averaged 17.0 points per game and 3.7 assists per game. In his NBA career, he played in 534 games and scored a total of 6,470 points.