Giles attended Wesleyan Christian Academy in High Point, North Carolina, where he was coached by Keith Gatlin.

[3] He also participated in the Under Armour Elite 24 game in Brooklyn, New York, finishing with 16 points and 11 rebounds and earning Co-MVP honors.

[5] On November 14, 2014, In his second game back since his injury, Harry scored a career-high 38 points and grabbed 19 rebounds in an 82–58 win over Northside Christian Academy.

[10] On January 15, 2015, Giles scored 17 points, 12 rebounds, and 4 assist to help the Trojans defeat Malik Monk and Bentonville High School (63–55).

[12] At the end of his junior season, Giles earned first-team All-USA honors by USA Today.

[17] Before his senior season, Giles decided to attend and play for the high school basketball powerhouse Oak Hill Academy in Mouth of Wilson, Virginia.

[18] Giles dominated the majority of his high school career; however, his senior year ended with a torn ACL in his right knee.

[20] Weeks later, Giles enrolled to (now-defunct) Forest Trail Academy in Kernersville, North Carolina to take online courses to finish his senior year of high school while rehabbing from his knee injury.

[22][23][24] He was selected to play in the 2016 Jordan Brand Classic and Nike Hoop Summit but was unable due to injury.

[39][40] On March 10, 2017, in the ACC tournament semi-finals against rival North Carolina, Giles had 4 blocks, 7 rebounds, and 6 points in a (95–83) win.

[41] On March 11, 2017, Giles contributed to 4 points and 4 rebounds in a 75–69 victory over Notre Dame in the ACC Tournament Championship game.

[45] At the conclusion of his freshman season, Giles announced that he would forgo his final three years of collegiate eligibility at Duke and enter the 2017 NBA draft.

In his NBA debut on October 17, 2018, Giles scored 2 points in a 123–117 season-opening loss against the Utah Jazz.

[66] Giles is good friends with former Duke teammate and current NBA player Jayson Tatum.