He attended Brunswick High School in nearby Lawrenceville, where he played basketball for former Virginia and NBA shooting guard Bryant Stith.

[1] As a senior, Green averaged 18.6 points, 5.8 rebounds, 2.3 assists and 3.1 steals per game and led the Bulldogs to the VHSL Group AA Division 3 state title.

Green entered the starting lineup as a freshman, averaging 10.2 points, 6.7 rebounds and 1.4 steals per game and was named to the Big South Conference's All-Newcomer team.

[6] As a sophomore, his first full season as a starter, Green led the Highlanders with 14.6 points and 8.1 rebounds per game and was named Second Team All-Big South.

[8] As a senior, Green averaged 15.4 points, nine rebounds, and 1.9 steals and was again named First Team All-Big South as well as the conference Defensive Player of the Year.

[20][21] After averaging 9.3 points (on 80% shooting) and 4.0 rebounds in 14.1 minutes played per game in the preseason, Green was named to the Celtics final roster going into the 2019–20 season.

[22] Green made his NBA debut on October 25, 2019, against the Toronto Raptors, playing the last five seconds of the first half as a defensive replacement in a 112–106 win.

[25] Green made his first NBA start on February 3, 2020, against the Atlanta Hawks, grabbing three rebounds with one assist and no points in 18 minutes played.

[26] On August 25, 2020, Green underwent successful arthroscopic procedure in repairing a small meniscal tear in his right knee and missed the postseason.