Johnson spent 16 years in the National Basketball Association as a player, and subsequently served as the head coach of two NBA teams: the Dallas Mavericks and New Jersey/Brooklyn Nets.

During his playing days, Johnson was known as the "Little General" for his small stature (by NBA standards), his leadership skills as a point guard, and his close friendship with former San Antonio Spurs teammate David Robinson.

After playing 21 games, Johnson was waived from the Nuggets in December before signing with the San Antonio Spurs on January 17, 1991.

[4] In the beginning of the 1991–92 season, Johnson played 20 games and averaged 5.0 points and 6.8 assists for the Spurs before being waived in December.

Promoted to starter, Johnson averaged 8.7 points, 1.9 rebounds, and 7.5 assists and improved his field goal percentage to .502 in 75 games.

[8] The Nuggets traded Johnson, Nick Van Exel, Raef LaFrentz, and Tariq Abdul-Wahad to the Dallas Mavericks on February 21, 2002, for Donnell Harvey, Tim Hardaway, Juwan Howard, and draft considerations.

During the 2003 offseason, the Mavericks traded Johnson, Van Exel, Popeye Jones, Antoine Rigaudeau, and Evan Eschmeyer to the Golden State Warriors for Antawn Jamison, Jiří Welsch, Chris Mills, and Danny Fortson.

[8] On October 28, 2004, Johnson retired from playing and signed as an assistant coach with the Dallas Mavericks under Don Nelson.

In June 2006, after defeating the Memphis Grizzlies, the defending champion San Antonio Spurs, and the Phoenix Suns in the first three rounds of the playoffs, Johnson led the Mavericks to their first ever NBA Finals appearance.

On December 31, 2006, Johnson became the fastest head coach (at the time) to win 100 games when his squad defeated the Denver Nuggets.

[12] On June 10, 2010, Johnson was hired as head coach of the New Jersey Nets,[13] which had just finished a dismal 2009–10 campaign with a 12–70 record.

In his first year as coach of the Nets, the team improved slightly, doubling its win total from the previous season and finishing 24–58.

Despite that early success, the team went on to lose ten of its next 13 games, and subsequently Johnson was fired from his head coaching position on December 27, 2012.

[16] On April 5, 2015, ESPN reported that Johnson had verbally agreed to become the new head basketball coach at the University of Alabama, replacing Anthony Grant.

[18] After losing in the first round of the 2019 National Invitation Tournament, Alabama and Johnson agreed to mutually part ways.