[2] On the Amateur Athletic Union circuit, Harper competed for Ring City Basketball, a program owned by his parents.

[6] In his senior season, he averaged 20.8 points and 3.9 rebounds per game, leading his team to its second straight Non-Public A state championship.

[7] He scored a career-high 33 points in a loss to Roselle Catholic High School at the Tournament of Champions final.

[11] On November 27, Harper scored a career-high 30 points with five-three pointers in a 96–75 win over Fairleigh Dickinson.

[17] Following Rutgers' loss in the First Four of the 2022 NCAA men's basketball tournament, Harper announced his intention to forgo his final season of collegiate eligibility and declare for the 2022 NBA draft.

[19] On July 14, 2022, after being undrafted in the 2022 NBA draft, Harper signed a two-way contract with the Toronto Raptors.

[25][26] After joining them for the 2024 NBA Summer League,[27] Harper signed with the Boston Celtics on July 14, 2024,[28] but was waived on October 17.

[33][34] His mother, Maria (née Pizarro), is from Bataan, Philippines and played college basketball for New Orleans, before becoming a coach.

[35] Harper has expressed interest in playing for the Philippines national basketball team but was unsuccessful when he tried to apply for a Filipino passport as a high school student.