On August 2, 2005, Williams and teammate James Posey were two of thirteen players involved in the biggest trade in league history that saw them being dealt to the Miami Heat in exchange for shooting guard Eddie Jones.

Williams started at point guard for the Heat in the 2005–06 campaign, playing a total of 59 games due to a knee injury but placing second only to Dwyane Wade in minutes per game.
He would serve as the third leading scorer for Miami averaging 12.3 points a game, only trailed Wade with 4.9 assists per contest and was one of three players on the team with over 100 three-point baskets for the season.
In the playoffs his averages were lower than the regular season, but he scored in double figures 11 times in the post-season including 21 points on 10 of 11 shooting in Game 6 of the Eastern Finals against the Detroit Pistons.
Miami closed out Detroit in that game and would win the NBA Championship over the Dallas Mavericks, giving Williams his first and only title.

In the 2006–07 season, Williams was limited to 61 games, of which he started 55.
He averaged 10.9 points and 5.3 assists, which did not meet his career averages of 11.7 and 6.5.
His play dropped dramatically in the postseason, averaging 5.8 points per game and 3.5 assists per game.
His struggles contributed to the Heat being swept by the Bulls in four games in the first round of the playoffs.

In the 2007–08 season, Williams played 67 games while averaging 8.7 points and 4.6 assists per game.
He shot 41.5 percent from the field, 86.3 percent from the free-throw line, and 35.3 percent from beyond the three-point arc.
In March, he had 34 points versus Orlando, connecting on five three-point baskets.
He had two double-doubles: one against Phoenix and one against the Bucks; both were 21-point, 10-assist performances.
On August 2, 2005, Williams and teammate James Posey were two of thirteen players involved in the biggest trade in league history that saw them being dealt to the Miami Heat in exchange for shooting guard Eddie Jones.
Williams started at point guard for the Heat in the 2005–06 campaign, playing a total of 59 games due to a knee injury but placing second only to Dwyane Wade in minutes per game. He would serve as the third leading scorer for Miami averaging 12.3 points a game, only trailed Wade with 4.9 assists per contest and was one of three players on the team with over 100 three-point baskets for the season. In the playoffs his averages were lower than the regular season, but he scored in double figures 11 times in the post-season including 21 points on 10 of 11 shooting in Game 6 of the Eastern Finals against the Detroit Pistons. Miami closed out Detroit in that game and would win the NBA Championship over the Dallas Mavericks, giving Williams his first and only title.
In the 2006–07 season, Williams was limited to 61 games, of which he started 55. He averaged 10.9 points and 5.3 assists, which did not meet his career averages of 11.7 and 6.5. His play dropped dramatically in the postseason, averaging 5.8 points per game and 3.5 assists per game. His struggles contributed to the Heat being swept by the Bulls in four games in the first round of the playoffs.
In the 2007–08 season, Williams played 67 games while averaging 8.7 points and 4.6 assists per game. He shot 41.5 percent from the field, 86.3 percent from the free-throw line, and 35.3 percent from beyond the three-point arc. In March, he had 34 points versus Orlando, connecting on five three-point baskets. He had two double-doubles: one against Phoenix and one against the Bucks; both were 21-point, 10-assist performances.
Jason Williams (basketball, born 1975)