Thompson made her international breakthrough in 2015. She repeated as Jamaican intercollegiate champion in March and broke 11 seconds for the first time at the UTech Classic on 11 April, running a world-leading 10.92. She then ran 10.97 at the Jamaica International Invitational in Kingston, defeating a field that included Blessing Okagbare and Allyson Felix; the win confirmed her new status as one of the world's leading sprinters. At the Pre Classic in Eugene Thompson was narrowly beaten by English Gardner in the B-race as both were timed in 10.84; as of 27 July 2015, which was Thompson's personal best in the 100 m and ranked her 30th on the world all-time list.
At the London Grand Prix on 25 July 2015 Thompson won a non-Diamond League 200 m race in 22.10, defeating Americans Tori Bowie and Candyce McGrone; the time was her new personal best and broke Merlene Ottey's meeting record from 1991. At the 2015 World Championships held in Beijing, Thompson won the silver medal, behind Dafne Schippers. Thompson's time of 21.66 was faster than the previous championships record but 0.03 slower than Schippers.