On February 28 of 1988, Johnson and teammate Mark West were traded to the Suns, where he avegared 18.8 points and 9.5 assists a game for the next 10 years. He became an all star three times and was part of a team that made it to the playoffs every year he was there. He also played with the Suns in the 1993 NBA finals, where they lost to the Chicago Bulls in six games.
Johnson retired after the 1996-1997 season, and was accused by a 17 year old girl of joining her while she was naked in his mansion, taking a shower. Johnson was never charged with the incident.
Johnson returned briefly during the '97-1998 campaign, helping the Suns win 13 games in a row by the season's end and clinch the last available playoff spot by one game. After losing in the playoffs, he re-retired.
In 2001, Johnson had his number retired during a game where the Suns lost to the Sacramento Kings, Johnson's hometown team.
While he was a Suns player, he would often sign free autographs at mall autograph shows. During his time with the Suns, he opened St. Hope Academy, a school for inner-city children in his hometown of Sacramento.