[1] His sophomore year, he transferred to Hillcrest Prep in Phoenix, Arizona, where he was teammates with future #1 pick Deandre Ayton.

[9] Bagley was rated as a five-star recruit throughout his high school career and was formerly ranked as the top player in the 2018 class before his reclassification.

[23] On November 24, Bagley scored 34 points and made a freshman record 15 rebounds for Duke as they defeated Texas 85–78 in overtime.

[24] He tied the freshman record for rebounds in the next game four days later and scored 30 points in an 87–84 win over Florida, It was the first time a Duke player did so since the 1960s.

Following Duke's loss in the 2018 NCAA men's basketball tournament, Bagley announced his intention to forgo his final three seasons of collegiate eligibility and declare for the 2018 NBA draft.

[34] On June 21, 2018, Bagley was selected second overall in the 2018 NBA draft by the Sacramento Kings, behind his former high school teammate Deandre Ayton.

[36] Bagley made his professional debut with Sacramento on October 17, 2018, with 6 points and 5 rebounds in only 12 minutes coming off the bench in a 123–117 loss to the Utah Jazz.

[42] On March 19, 2019, Bagley scored a career-high 28 points off the bench in a 123–121 loss to the Brooklyn Nets, in which the Kings entered the fourth quarter with a 25-point lead.

[51][52] On February 25, 2023, after missing over a month with a hand injury, Bagley scored 21 points and grabbed 18 rebounds during a 95–91 loss to the Toronto Raptors.

[53] On January 14, 2024, Bagley was traded to the Washington Wizards, along with Isaiah Livers and future draft considerations in exchange for Danilo Gallinari and Mike Muscala.

While living in the Los Angeles area, Bagley volunteered at Hoops with Heart, a non-profit organization in the city that benefits underprivileged youth.

[60] He is also the grandson of former Olympic and professional basketball player Jumpin' Joe Caldwell, who was the number two overall pick in the 1964 NBA draft.

His album Big Jreams was released on August 24, 2019, featuring other artists including Iman Shumpert and Famous Los.