Shareef Rashaun O'Neal was born on January 11, 2000.
In May 2015, Shareef O'Neal received his first NCAA Division I scholarship offer from USC.
In October 2015, at a high school basketball tournament at Fairfax High School, Shareef O'Neal scored 23 points in a game against Bishop Alemany High School.
On June 29, 2016, it was announced that Shareef O'Neal would be transferring to Crossroads School in Santa Monica.
On January 6, 2017, Shareef O'Neal and Crossroads School won against Brentwood School in basketball with a score of 54-50. O'Neal scored 15 points during the game.
In April 2017, Shareef O'Neal committed to play college basketball at the University of Arizona.
On February 24, 2018, Shareef O'Neal withdrew his commitment to play basketball for the University of Arizona following allegations against the team's coach.
On September 28, 2018, it was announced that Shareef O'Neal would have to miss the 2018-2019 basketball season to undergo heart surgery after being diagnosed with a heart condition.
In April 2019, Mick Cronin replaced Steve Alford as the head coach of the UCLA Bruins men's basketball team.
Shareef O'Neal had his then career-high in rebounds on December 14, 2019, in a game against Notre Dame, with 11 rebounds and 8 points.
In 2019, Shareef O'Neal made his debut with the UCLA Bruins, playing as a reserve.
On January 19, 2020, Shareef O'Neal was benched during a game against California.
On February 14, 2020, Shareef O'Neal announced he would be transferring to Louisiana State University.
During the 2020-2021 season, Shareef O'Neal suffered a foot injury that affected his playing time. He was limited to 10 games that season.
On June 6, 2022, Shareef O'Neal declared for the NBA draft after being mistakenly placed on the list of players withdrawing.
On September 28, 2022, Shareef O'Neal signed with the NBA G League Ignite.