Quinn Costello is an American high school basketball player who attends The Newman School. He is a four-star recruit signed to play college basketball for the Michigan Wolverines.
Costello attends The Newman School in Boston, and the Middlesex Magic on the Under Armour Association circuit. During his senior year, he averaged 16.4 points and 8.1 rebounds per game midseason. On November 15, 2025, he scored 17 points and 15 rebounds for his first double-double of the season. On November 22, 2025, he scored a career-high 36 points at the National Prep Showcase.
On February 2, 2026 he was named to the 2026 McDonald's All-American Boys Game. He was Michigan's second McDonald's All-American in as many years, following Trey McKenney's selection in 2025, and the 25th overall in program history.
On September 16, 2025, Costelllo committed to play college basketball for Michigan, over offers from Michigan State, Minnesota, North Carolina, Purdue and Texas. He was rated as the No. 1 player in the state of Massachusetts by 247Sports and ESPN. ESPN ranked Costello as a top 30 player overall in the nation.