He played college basketball for Louisiana State University before being selected by the Celtics with the 33rd overall pick in the 2015 NBA draft.

[4] In the second round of the NCAA Tournament, he tallied 12 points, 14 rebounds and six blocks, but the Tigers were edged by North Carolina State, 66–65.

[6] On July 20, he signed with the Celtics after playing for the team at the Utah and Las Vegas summer leagues.

[7] Over the first two and a half months of the 2015–16 season, Mickey spent the majority of his time in the NBA Development League playing for the Maine Red Claws, Boston's affiliate team in the D-League.

[13] However, he was ruled out of the All-Star game due to his left ankle injury and was replaced in the East team by Keith Benson.

[26] On July 26, 2018, Mickey signed a one-year deal with the Russian team BC Khimki of the VTB United League and the EuroLeague.

[32] On July 13, 2022, Mickey signed with Virtus Bologna of the Italian Lega Basket Serie A and the EuroLeague.

[33] On 29 September 2022, after having ousted Olimpia Milano in the semifinals, Virtus won its third Supercup, defeating 72–69 Banco di Sardegna Sassari and achieving a back-to-back, following the 2021 trophy.

In June, after having ousted 3–0 both Brindisi and Tortona, Virtus was defeated 4–3 by Olimpia Milan in the national finals, following a series which was widely regarded among the best in the latest years of Italian basketball.

[36][37] On 24 September 2023, after having ousted Olimpia Milano in the semifinals, Virtus won its fourth Supercup, and the third in a row, defeating 97–60 Germani Brescia.

[38] On November 6, 2024, Mickey signed with Qingdao Eagles of the Chinese Basketball Association (CBA),[39] replaced Akil Mitchell.