Stewart was born in Rochester, New York. He grew up playing soccer and boxing. Starting in fifth grade, Stewart focused on basketball, which he was drawn to because of his size and athleticism. He played organized basketball for the first time at age 10, while attending elementary school in Rochester. At age 12, Stewart stood around.
High school career
Stewart attended McQuaid Jesuit High School in his first two years of high school. When he was 14 years old, as a freshman, he stood. In his freshman season, Stewart averaged 18.5 points, 12.4 rebounds and 3.1 blocks per game, recording two back-to-back 40-point games, and was named Rochester City Athletic Conferenceplayer of the year. In October 2016, he broke his tailbone during United States national under-16 team tryouts and consequently missed most of his sophomore season. On February 2, 2017, Stewart returned to the court, posting 35 points, 14 rebounds, and six blocks in his season debut. Entering his junior year, Stewart transferred to La Lumiere School, a prep school in La Porte, Indiana with a prestigious basketball program. In 19 games, he averaged 19.8 points, 11.2 rebounds, and 2.4 blocks per game, leading his team to a 25–4 record. Stewart earned MaxPreps Junior All-American honorable mention recognition. In his senior season with La Lumiere, he averaged 18.1 points, 11.3 rebounds, and 2.9 blocks per game, helping his team to a 30–1 record. Stewart won the Naismith Prep Player of the Year and Mr. Basketball USA awards. He was named to the USA Today All-USA first team and MaxPreps All-American second team. Stewart played in the McDonald's All-American Game, Jordan Brand Classic, and Nike Hoop Summit.
Recruiting
Stewart finished his high school career as a consensus five-star recruit and top-five player in the 2019 class. On January 21, 2019, he committed to play college basketball for Washington. The other finalists to land him were Duke, Kentucky, Michigan State, and Syracuse. Stewart was drawn to Washington because of his longtime relationship with Mike Hopkins. He knew Hopkins, a former Syracuse assistant coach, since his time playing for McQuaid Jesuit.
College career
Stewart made his collegiate debut against the Baylor Bears in the 2019 Armed Forces Classic, recording 15 points and seven rebounds, including the game-winning basket in a 67–64 victory. At the conclusion of the regular season, Stewart was named to the All-Pac-12 first team and the Freshman Team. Stewart posted 29 points and 12 rebounds against Arizona in the Pac-12 tournament. He averaged 17 points, 8.8 rebounds and 2.1 blocks per game for the Huskies. Following the season Stewart declared for the 2020 NBA draft.
Stewart's father Dela Stewart, who is a native of Jamaica, emigrated to the United States in the early 1970s for farm work. Later on, he moved to New York, where he met Stewart's mother Shameka Holloway and began working in construction. Stewart's paternal grandfather, who was a Jamaican fisherman and farmer, stood. Stewart has worn the number 33 basketball jersey in honor of Jamaican former National Basketball Association player Patrick Ewing.
