He played one year of college basketball for the Kentucky Wildcats and was selected 11th overall by the Charlotte Hornets in the 2018 NBA draft before being traded to the Los Angeles Clippers that same night.

[3] His mother, Charmaine Gilgeous, is a former track athlete, who competed in the women's 400 metres for Antigua and Barbuda at the 1992 Summer Olympics.

He then moved to the United States, transferring to Hamilton Heights Christian Academy (located in Chattanooga, Tennessee) for his junior and senior years to improve his basketball skills, graduating in 2017.

[7][8] Growing up in Hamilton, he did not make the St. Thomas More junior team in grade 9 and subsequently played on the school's midget squad.

[5] He then attended Sir Allan MacNab Secondary School before heading to Hamilton Heights Christian Academy in Chattanooga, Tennessee, in 2015.

[14] At the 2017 Nike Hoop Summit, he represented the World Select Team and scored eleven points in 21 minutes of action.

[15] Gilgeous-Alexander started the 2017–18 season as a reserve, sitting behind freshman point guard Quade Green, but still averaged over 30 minutes per game.

After a tough loss to UCLA, Alexander erupted against Louisville in December, scoring 24 points, grabbing 5 rebounds, dishing out 4 assists, and securing 3 steals.

[26][27] On December 26, 2020, Gilgeous-Alexander put up 24 points, seven rebounds, nine assists, and a game-winning jump shot in a 109–107 win against the Charlotte Hornets.

[28] On February 24, 2021, Gilgeous-Alexander scored a then career-high 42 points to give the Oklahoma City Thunder a 102–99 win over the San Antonio Spurs.

[31] On December 18, 2021, Gilgeous-Alexander scored 18 points and made a game-winning three-pointer at the buzzer to lift the Thunder over his former team, the Los Angeles Clippers, 104–103.

[36] On November 16, Gilgeous-Alexander tied a then career-high with 42 points, alongside a game-winning three-pointer, six rebounds and seven assists, in a 121–120 win over the Washington Wizards.

[42] Shai became the second guard in NBA history behind Michael Jordan to average at least 30 points, four rebounds, four assists, one steal and one blocked shot while shooting at least 50 percent from the field.

He subsequently became the youngest guard in NBA history to average 30 points on 50 percent from the field beating Jordan's record.

[46] On November 8, 2023, Gilgeous-Alexander scored 43 points on 15-of-22 shooting from the field and 12-of-13 from the free throw line in a 128–120 win over the Cleveland Cavaliers.

[49] On December 16, Gilgeous-Alexander put up 25 points, six rebounds, eight assists, two steals, and a game-winning mid-range jumpshot in a 118–117 win over the Denver Nuggets.

[56] On November 11, 2024, Gilgeous-Alexander scored a career-high 45 points, along with three rebounds, nine assists, five steals and two blocks in a 134–128 win over his former team, the Los Angeles Clippers.

[57] On December 26, Gilgeous-Alexander tied his career-high with 45 points on 15-of-22 shooting, 4-of-5 from three, 11-of-11 from the free throw line, along with seven rebounds, eight assists, one steal and two blocks in a 120–114 win over the Indiana Pacers.

[58] During the month of December, Gilgeous-Alexander led the Thunder to a 12–1 record while averaging an NBA-best 33.3 points on 56.3% shooting from the field to go along with 5.8 rebounds, 5.2 assists, 2.5 steals and 1.2 blocks per game.

[61][62] On January 22, Gilgeous-Alexander recorded a career-high 54 points, eight rebounds, five assists, three steals and two blocks in 123–114 win over the Utah Jazz.

[66][67] Gilgeous-Alexander played for the Canadian junior national team that competed in the 2016 FIBA Americas Under-18 Championship in Valdivia, Chile, averaging 7.8 points, 5.4 assists, and 4.0 rebounds per contest, en route to winning a silver medal.

[70] On May 24, 2022, Gilgeous-Alexander was one of fourteen players to agree to a three-year commitment to play with the national team, aiming to break a decades-long trend of failing to qualify for the Olympic basketball tournament.

[71] At the 2023 FIBA World Cup, Gilgeous-Alexander was the central figure on the Canadian roster, leading them on a historic deep run.

[89] In spring 2023, Gilgeous-Alexander purchased a lakefront property in Burlington, Ontario previously occupied by bankrupt cryptocurrency trader Aiden Pleterski.