Williams was born in Lancaster, California as the only child of Ziaire Williams and Marquita Fields-Williams. He began playing basketball at age five and was training under the guidance of his father by age eight.
High school career
For his first three years, Williams attended Notre Dame High School in Sherman Oaks, Los Angeles. In his freshman season, he averaged 13.6 points and 6.5 rebounds per game. Williams missed much of his sophomore season with an injury but saw success in the summer with his club team BTI Select. On January 14, 2019, as a junior, he was named Los Angeles Daily News boys athlete of the week following two consecutive games with at least 34 points. In his junior season, Williams averaged 27 points, 10 rebounds, and three assists per game. He earned All-Mission League first team and USA Today All-USA California second team honors. On July 18, 2019, Williams transferred to Sierra Canyon School in Chatsworth, Los Angeles. He joined the team with fellow five-star recruit BJ Boston, as well as Bronny James and Zaire Wade, the respective sons of basketball players LeBron James and Dwyane Wade. Williams was not eligible to play until December 29, due to CIF Southern Section transfer rules, and missed more than 10 games. In his season debut, he scored 28 points in an 85–81 overtime loss to Rancho Christian School. On March 11, 2020, Williams scored 17 points and made a buzzer-beater in a 63–61 comeback win over Etiwanda High School. As a senior, he averaged 15 points, 7.9 rebounds and 3.6 assists per game, helping Sierra Canyon win the CIF-SS Open Division title. He was named player of the year by the Los Angeles Times. Williams was selected to play in the McDonald's All-American Game, Jordan Brand Classic and Nike Hoop Summit, but all three games were canceled due to the coronavirus pandemic.
Recruiting
Williams is a consensus five-star recruit and the number one small forward in the 2020 recruiting class. On April 12, 2020, he announced his commitment to Stanford over Arizona, USC, North Carolina and UCLA. Williams became Stanford's highest-ranked recruit in the modern recruiting era and the program's first five-star recruit since Reid Travis in 2014.
Both of Williams' parents have served in the military: his mother, Marquita Fields-Williams, in the Army and Air Force, and his father, Ziaire Williams, in the Marine Corps. His mother is a probation officer, and his father works for 7 Up in Sylmar, Los Angeles.
