In 2018, Gillespie won the PAC-12 100m title and finished second in the 200m. He qualified for the 100m final at the Outdoor NCAA Championships, where he finished fourth in 10.27 seconds.
2019
After finishing 4th in the 60m at NCAA Indoors, Gillespie's breakthrough came outdoors; he defended his PAC-12 100m title in 9.97 seconds, breaking 10 seconds for the first time. He also won the 200m in 20.17 seconds. At NCAAs, he was second in both 100m and 200m, setting Oregon school records of 9.93 and 19.93 seconds, respectively.
International career
2019
On June 14, 2019, just seven days after his breakthrough NCAA performances, Gillespie turned professional and signed with Nike. He focused on the 100 metres for the rest of the season, finishing fourth at the US Championships and qualifying for the US' World Championship 4 × 100 metres relay team. He was also selected to represent USA at the 2019 Pan American Games, where he finished sixth in the 100 metres and won bronze in the 4 × 100 metres relay.[2]
Gillespie was scheduled to compete in the 100 meters at the 2019 World Athletics Championships.[3] He ultimately did not race individually, but did race as part of the 4 × 100 metres relay heats; he did not race in the relay final, but due to racing in the heats was awarded a gold medal.[4]
He entered the Championships with a tie for the fifth fastest time in the world.[5]
2020
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.
2021
After a rocky start to his season, Gillespie returned to Mt. San Antonio for the USATF Golden Games, where he would compete against Seattle Seahawkswide receiverDK Metcalf in the 100 metres. He won his heat with ease in 10.11 seconds, then won the final in a season's best of 9.96 seconds; his first sub-10 since NCAAS two years prior. He then set his sights on the Olympic Trials, where he finished sixth in 10.00 seconds. 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.
