[2] Born in Salisbury, North Carolina, Williamson attended Spartanburg Day School, where he was a consensus five-star recruit and was ranked among the top five players in the 2018 class.

[6] He competed in youth leagues with his mother Sharonda Sampson coaching and played for the Sumter Falcons on the Amateur Athletic Union (AAU) circuit, facing opponents four years older than he was.

[6] He joined the basketball team at Johnakin Middle School in Marion, South Carolina, where he was again coached by his mother and averaged 20 points per game.

[11] He also led Spartanburg Day to a South Carolina Independent School Association (SCISA) state championship game appearance.

[12] In his sophomore season, Williamson averaged 28.3 points, 10.4 rebounds, 3.9 blocks, and 2.7 steals per game and was named SCISA Region I-2A Player of the Year.

[18] In a 73–53 victory over Gray Collegiate Academy at the Chick-fil-A Classic on December 21, he posted a tournament-record 53 points and 16 rebounds, shooting 25-of-28 from the field.

[19] On December 30, Williamson recorded 31 points and 14 rebounds to win most valuable player (MVP) at the Farm Bureau Insurance Classic.

[22] On February 14, he led Spartanburg Day past Oakbrook Prep for their first SCISA Region I-2A title, chipping in a game-high 37 points in a 105–49 rout.

[28] On January 13, 2018, in a nationally televised game at the Hoophall Classic, he scored 36 points as his team lost to Chino Hills High School.

[30] One week later, Williamson guided Spartanburg Day to its third consecutive SCISA Region I-2A championship after recording 38 points against Trinity Collegiate School.

[39] By the end of his sophomore season, he had received offers from 16 NCAA Division I programs, including Clemson, Florida, and South Carolina.

[45] Sources: On November 6, 2018, in his first regular season game with Duke, Williamson scored 28 points on 11-of-13 shooting in 23 minutes in a 118–84 win over Kentucky at the Champions Classic.

[46] In that game, he and teammate RJ Barrett each broke the Duke freshman debut scoring record set by Marvin Bagley III.

[51] On January 12, against Florida State, he was poked in the left eye by an opposing player towards the second half and missed the remainder of the game.

[53] He eclipsed the Duke freshman record for single-game points previously held by Marvin Bagley III and JJ Redick.

[60] In a February 20 game versus North Carolina, Williamson suffered a Grade 1 knee sprain 36 seconds into the contest after his foot ripped through his Nike shoe, causing him to slip.

[72] Williamson returned from injury on March 14, posting 29 points, 14 rebounds, and 5 steals in an 84–72 win over Syracuse in the quarterfinals of the ACC tournament.

[75] The next day, he scored 31 points (including the game-winning shot) to help Duke defeat North Carolina, 74–73, in the ACC Tournament semifinals.

[76] After posting 21 points in a 73–63 victory over Florida State in the championship game, Williamson was named ACC Tournament MVP, becoming the sixth freshman to win the honor.

[83][84] In addition, Williamson joined Kevin Durant and Anthony Davis as one of the only freshmen in history to collect 500 points, 50 steals, and 50 blocks in a season.

[109] Williamson made his return from injury on October 4, 2022, putting up 13 points, four rebounds, one assist, and one steal in a 129–125 preseason win over the Chicago Bulls.

[110] On October 19, Williamson made his regular season return, putting up 25 points, nine rebounds, three assists, and four steals in a 130–108 win over the Brooklyn Nets.

[111] On December 2, Williamson scored 30 points and matched career highs with 15 rebounds and eight assists in an 117–99 win over the San Antonio Spurs.

[120] Subsequently, Williamson sat out the Pelicans appearance in their play-in game against the Oklahoma City Thunder, which New Orleans lost, ending their season.

[121] On November 29, 2023, Williamson recorded 33 points on 11-of-12 shooting from the field, 11-of-12 from the free throw line along with eight rebounds, six assists, and three steals in a 124–114 win over the Philadelphia 76ers.

[123] On April 16, Williamson in his first play-in appearance scored 40 points, grabbed 11 rebounds and dished out 5 assists in a 110–106 loss against the Los Angeles Lakers.

[129][130] NBA player Kevin Durant described him as a "once-in-a-generation type athlete" while an anonymous college basketball coach labeled him a "freak of nature.

[134] His physical attributes have drawn comparisons to former NBA stars Charles Barkley, Anthony Mason, and Larry Johnson.

[155] On March 13, 2020, Williamson pledged to pay for the salaries of all the employees of the Smoothie King Center for 30 days during the suspension of the 2019–20 NBA season, which was caused by the COVID-19 pandemic.

[156] In June 2023, Williamson announced his girlfriend's pregnancy in a baby shower YouTube video with the couple expecting a daughter due in November.