In 2014, he helped Montverde win back-to-back High School National Tournament championships playing alongside Ben Simmons.

On April 22, 2015, Russell declared for the NBA draft, forgoing his final three years of college eligibility.

[9] In his debut for the Lakers in their season opener on October 28, 2015, Russell recorded four points, three rebounds and two assists in just under 26 minutes in a 112–111 loss to the Minnesota Timberwolves.

[14] His eight three-pointers broke Nick Van Exel's previous rookie Laker record of six in a single game.

[19][20] On January 31, he recorded his second career double-double with 22 points, a career-high 10 assists and seven rebounds in his return from a three-game absence with a pair of mild leg injuries, helping the Lakers defeat the Denver Nuggets by a score of 120–116.

[23] On June 22, 2017, Russell was traded, along with Timofey Mozgov, to the Brooklyn Nets in exchange for Brook Lopez and the rights to Kyle Kuzma, the 27th pick in the 2017 NBA draft.

[46] On March 19, Russell scored 27 of his career-high 44 points in the fourth quarter, keying the Nets' 123–121 win over the Sacramento Kings after trailing by as many as 28.

[49] Russell helped the Nets finish the regular season as the sixth seed in the Eastern Conference with a 42–40 record.

In Game 1 of the Nets' first-round playoff series against the Philadelphia 76ers, Russell scored 26 points in his postseason debut to lead Brooklyn to a 111–102 win.

[50] On June 28, 2019, the Nets extended a qualifying offer to Russell in order to make him a restricted free agent.

[51] On July 7, 2019, Russell, Shabazz Napier, and Treveon Graham were traded to the Golden State Warriors as part of a sign-and-trade package for Kevin Durant.

[57] On February 24, 2022, Russell led the Timberwolves to a 119–114 victory over the Memphis Grizzlies by scoring a season-high 37 points, along with 9 assists.

[58] In the Play-In game on April 12, 2022, Russell scored 29 points to lead them to a victory over the Los Angeles Clippers after Karl-Anthony Towns fouled out with 7 minutes left to go.

On November 13, 2022, Russell scored a season-high 30 points and delivered 12 assists, shooting 11-of-13 from the field, including 4-of-5 from beyond the arc in a 129–124 win over the Cleveland Cavaliers.

[60] On February 11, Russell made his Lakers return, putting up 15 points, five rebounds, and six assists in a 109–103 win over his former team and the reigning champions Golden State Warriors.

The incident occurred following the conclusion of the Lakers' 145–144 double-overtime victory over the Golden State Warriors two days prior at Chase Center.

[66] On March 8, Russell scored a season-high 44 points, grabbed 6 rebounds and delivered 9 assists, alongside a game-winning floater in a 123–122 victory against the Milwaukee Bucks.

[67] On March 22, in a game against the Philadelphia 76ers, Russell broke a tie with Nick Van Exel for the most three-pointers made in a single season by a player in Lakers franchise history, with 184.

[68] On December 29, 2024, Russell was traded back to the Brooklyn Nets, alongside Maxwell Lewis and three second-round draft picks, in exchange for Dorian Finney-Smith and Shake Milton.