He was selected by the Atlanta Hawks with the 18th overall pick in the 2013 NBA draft, where he was immediately traded to the Dallas Mavericks.

[2][3] After being told this training was "all wrong" by a Little League coach, Larkin quit baseball and decided to focus on basketball.

He ended up requesting a transfer before the start of his freshman year due to a then unnamed medical condition.

[6] He chose Miami, a school closer to home to help his anxiety and where he was introduced to meditation and relaxation techniques by a new therapist.

Larkin was selected to the All-ACC Freshman team at the conclusion of the season, finishing the year averaging 7.4 points, 2.5 assists, 2.5 rebounds, and 1.6 steals.

[9] Larkin was an important player in the team's success, playing some of his best games in many of the most crucial matchups of the season.

[10] Against North Carolina on February 9, Larkin shot 5 for 8 beyond the three-point line, had 9 assists, and delivered an alley-oop pass to Kenny Kadji off the backboard which prompted a standing ovation from Miami Heat players Dwyane Wade and LeBron James who were in attendance.

[14] On November 18, 2013, Larkin made his NBA debut, recording 3 points, 3 assists, and 3 steals in a 97–94 win over the Philadelphia 76ers.

[16] On April 23, he made his NBA postseason debut against the San Antonio Spurs in Game 2 of the Western Conference First Round.

[18] On June 25, 2014, Larkin was traded, along with Wayne Ellington, José Calderón, Samuel Dalembert and two 2014 second-round picks, to the New York Knicks in exchange for Tyson Chandler and Raymond Felton.

[22] He made his debut for the Nets in the team's season opener against the Chicago Bulls on October 28, recording six points and eight assists as a starter in a 115–100 loss.

[24] On February 1, he recorded eight points, a career-high 14 assists and six rebounds off the bench in a 105–100 loss to the Detroit Pistons.

[33] In the Celtics' regular season finale on April 11, 2018, Larkin had 12 points, 10 assists and seven rebounds in a 110–97 win over the Brooklyn Nets.

He said, “I will not go back to the NBA as a third point guard [...] So, if any team asks about that, we’re not even gonna answer the phone.”[35] On July 26, 2018, Larkin signed a one-year deal with Anadolu Efes of the Turkish Basketball Super League and the EuroLeague.

[36] On March 8, 2019, Larkin recorded a then career-high 37 points, shooting 12-of-15 from the field, along with five rebounds and two assists for 43 PIR in a 92–70 win over Barcelona.

[7] Larkin has stated that he views Turkey as "more of a home" when asked about the possibility of playing for the Turkish national team.