Bruce Weber assumed the head coach position for the Illini in April 2003 and helped develop Williams throughout his remaining collegiate career.

In 2005, as a junior starting point guard, Williams led the Fighting Illini to the NCAA championship game where they lost to the University of North Carolina.

In the fifth game, Williams was plagued by foul problems and struggled from the floor, hitting only one of eleven shots from the field and scoring just two points.

Williams played his best basketball of the season in the first three games, averaging nine assists and over thirty points over that span.

[23] Despite his strong performance during the season, he was not selected to represent the Western Conference in the NBA All-Star Game, as the point guard position was filled by Allen Iverson, Steve Nash, and Chris Paul.

[27] The Jazz again won the Northwest Division and the four seed, this time with a 54–28 record, and again faced a Houston Rockets team that had home-court advantage in the first round.

[30] Williams missed thirteen of the first fifteen games of the season due to a second-degree ankle sprain sustained in the preseason against the Chicago Bulls.

Similar to the previous year, he responded to the snub with strong play, scoring 30+ points in five consecutive games before the break (he missed one additional game during this time due to a minor injury) and leading the team to a 5–2 record to close out the first half of the season, including a win over the league-leading Los Angeles Lakers to snap their seven-game winning streak.

Williams scored 33 points on 7–14 shooting from the field while making 16–18 free throws from the line, while also contributing 14 assists on the road in a game 2 win against the Denver Nuggets.

On April 28, Williams became the first player in NBA history to record at least 20 points and 10 or more assists in five straight games in a playoff series.

"[36][37] On February 23, 2011, Williams was traded to the New Jersey Nets for guard Devin Harris, forward Derrick Favors, two first round draft picks, and $3 million in cash.

[39][40] Williams's acquisition gave the Nets a proven NBA star to build around as the team was preparing to make the transition to their new home in Brooklyn.

"[43] During the 2011 NBA lockout, Williams signed a one-year contract for $5 million net income to play for Beşiktaş of the Turkish Basketball League and the FIBA EuroChallenge.

[48] After a tentative agreement to end the 2011 NBA lockout was reached, Williams's jersey #8 was retired by Beşiktaş in a farewell ceremony prior to a game against Zorg en Zekerheid Leiden on November 29, 2011.

The Nets caught a bad break in the preseason, though, as Brook Lopez suffered a broken foot that caused him to miss more than 2 months.

After winning their opening game at Washington, the Nets went on to lose their next six, putting them in an early hole in the standings in an abbreviated season.

The Nets continued to struggle without Lopez, but Williams played well enough to be voted into the All-Star Game for the third time in his career, as he averaged over 22 points and 8 assists at the break.

Williams remained optimistic that he would resign with the Nets, but was noncommittal as he said he wanted to keep his options open and become a free agent at the end of the season.

[citation needed] Williams reiterated this stance on March 16 after the Nets failed to land All-Star center Dwight Howard at the trade deadline.

He was encouraged to stay with the Nets after GM Billy King completed a trade with the Atlanta Hawks for six-time All-Star Joe Johnson, as well as re-signing young big man Brook Lopez and defensive player Gerald Wallace.

[57] On March 28, 2014, Williams recorded his 21st consecutive game with at least one steal, tying the Hawks' Paul Millsap with the longest such streak in the league in 2013–14.

[62] The streak ended at 31 on April 22 after he failed to record a steal in Game 2 of their first-round playoff matchup against the Toronto Raptors.

[64] Despite a good start to the season injury-wise for Williams, he went down on December 19 in the 91–95 loss to the Cleveland Cavaliers, limping off the court in the second quarter with a strained right calf and did not return.

[65] He subsequently missed the following two games, only to return on December 26 against Boston coming off the bench for the first time this season, losing his starting spot in favor of Jarrett Jack.

[67] After an 11-game absence due to the injury, Williams returned to action on February 2 against the Los Angeles Clippers, recording 15 points and 3 assists off the bench in the 102–100 win.

[68] On February 20 against the Los Angeles Lakers, Williams regained his starting spot from Jack after 13 straight games coming off the bench.

[74] He made his debut for the Mavericks in the team's season opener against the Phoenix Suns on October 28, recording 12 points and 7 assists in a 111–95 win.

[82] In the Mavericks' season opener on October 26, 2016, Williams scored a team-high 25 points in a 130–121 overtime loss to the Indiana Pacers.

[92] Williams appeared in all 18 playoff games for Cleveland as the backup point guard to Kyrie Irving, en route to the NBA Finals, where they were defeated by the Golden State Warriors.

[99] Williams appeared as himself on the Disney Channel show The Suite Life on Deck during the season 3 episode Twister: Part 1 along with Dwight Howard and Kevin Love.