He represented the United States at the 2019 World Athletics Championships, earning a gold medal in the 4 × 100 metres relay.

Following stints at Monrovia High School and Mount San Antonio College, Gillespie became an All-American multiple times for the Oregon Ducks and Mt.

[5] On August 6, 2020, Gillespie won his first race as a professional at the PVAMU Back To The Track Series 3 in Prairie View, Texas.

San Antonio for the USATF Golden Games, where he would compete against Seattle Seahawks wide receiver DK Metcalf in the 100 metres.

He also competed in the 2020 Summer Olympics in Tokyo, Japan where he ran the anchor leg of the 4x100m relay team also featuring Trayvon Bromell, Fred Kerley, and Ronnie Baker.