He won the 2018 Horizon League Men's Basketball Player of the Year award at Oakland after leading the nation in three-point shots made per game.

In October 2023, Nunn signed with Panathinaikos and won the EuroLeague title in his first season in Europe, earning All-EuroLeague First Team honors in the process.

As a freshman, he received his first basketball scholarship offer from Rick Majerus, then the head coach at Saint Louis University.

[5] Nunn and Parker joined Derrick Rose, Bobby Simmons, and Benji Wilson as the only Wolverine basketball players to have their jersey numbers retired.

Nunn verbally committed to Texas A&M before his junior year in August 2011,[7] but about two months later he announced his de-commitment from that school and intent to reopen his recruiting process.

[9] He debuted as a starter on February 9, 2014, against Penn State, finishing the contest with 19 points and helping the team snap an eight-game losing streak.

[10][11] Nunn tied his career-high on February 19, with 19 points, to lead the Illini to a 62–49 victory at Minnesota;[12] for this performance, he was named the Big Ten Freshman of the Week five days later.

[13][14] On the heels of wins over Nebraska[15] and Michigan State,[16] in which Nunn averaged 10.5 points, 4.5 rebounds, and 3.5 assists, he repeated as the Big Ten Freshman of the Week on March 3.

[20] Nunn was dismissed from the Illinois basketball team on May 24, 2016,[21] after pleading guilty to a charge of misdemeanor battery two months earlier.

[25] While playing in the Golden Grizzlies' 2017–18 campaign, Nunn earned Horizon League Player of the Week on November 13 and did so again on December 18 and January 22.

[37] In his November 4 professional debut for the team, Nunn recorded 15 points in a 118–108 win versus the Northern Arizona Suns.

[42][43] His NBA debut came on October 23 in the Heat's season opener against the Memphis Grizzlies, when he started and had 24 points, 2 rebounds, 3 assists, and 2 steals during the 120–101 victory.

[48] On December 10, he posted a career-high 36 points to help the Heat secure a 135–121 overtime win versus the Atlanta Hawks.

[68] On January 23, 2023, Nunn was traded, alongside three future second-round draft picks, to the Washington Wizards in exchange for Rui Hachimura.

[69] Nunn made his Wizards debut two days later, recording 12 points, four rebounds, four assists and two steals off the bench in a 108–103 win over the Houston Rockets.

[77] Nunn, along with teammate Jabari Parker of Simeon and rival Jahlil Okafor of Whitney Young high school, was selected to play in the 2012 FIBA Under-17 World Championship held in Kaunas, Lithuania, from June 29 to July 8, 2012.