[7] He was the lone returning starter for the Ducks in his sophomore year (2017–18) and averaged a markedly higher 14.5 points, 4.8 assists and 3.6 rebounds per game.

On January 18, 2020, against Washington, he scored 22 points and made a 30-foot shot with three seconds left to complete a 16-point comeback as Oregon won in overtime 64–61.

[11] He scored a career-high 38 points in a narrow 73–72 overtime victory over Arizona on February 22 in a must-win game to keep Oregon's hopes for a Pac-12 regular season title alive.

[17] On November 24, 2020, he signed a four-year, $10.5 million rookie contract with the Boston Celtics including team options in the third and fourth years.

[20] In the absence of Kemba Walker, Pritchard was fourth in playing time through the first five games, behind only Jayson Tatum, Jaylen Brown and Marcus Smart.

[23] On January 12, Pritchard earned his first NBA start, but had an underwhelming performance, scoring only two points in 28 minutes in a 96–93 loss to the Detroit Pistons.

Pritchard alluded to his struggles later on in the season,[25] but seemingly burst through this looming "rookie wall" in mid-April when he scored in double figures in six of seven games in a row including a then-career-best 28 points in a 119–115 loss to the Oklahoma City Thunder on April 27.

[35] Pritchard joined John Havlicek, Larry Bird and Bob Cousy as the only players in franchise history to record back-to-back 30-point, 10-assist double-doubles.

[36] During Game 2 of the 2024 NBA Finals against the Dallas Mavericks on June 9, Pritchard made a 34-foot three-pointer at the buzzer to end the third quarter as the Celtics won 105–98.

[37][38] Eight days later in Game 5, he made a half-court shot at the buzzer to end the first half of the close-out 106–88 victory, giving Pritchard his first NBA championship.

Pritchard scored 12 points on four three-pointers in 14 minutes as a member of the USA National Select Team at the 2016 Nike Hoop Summit.