Josh Kerr has competed in national middle-distance competitions since 2012. In 2013 he ran a time of 3: 58.87 minutes over the 1500 meters, in which he has specialized since then. Another year later he won two gold medals in the British U17 championships, one over 1500 and one over 3000 meters. By May 2015 he had climbed the 1500 meters to a time of 3: 44.12 minutes. Shortly thereafter, after the U17 championship, he also became British U20 champion and competed in the U20 European Championships in Eskilstuna in July , where he won the gold medal in 3: 49.62 minutes. After graduating from high school, he moved to the United States, where he took a master's degree in sports science from the University of New Mexico and has since competed in college competitions for their sports team, the New Mexico Lobos. In 2016 he took part for the first time in the British Adult Championships, where he finished fourth over 1500 meters. In July he started at the U20 World Championships in Bydgoszcz over this distance . He reached the final and ended up in tenth place in 3: 51.23 minutes.
In April 2017, Kerr set a new personal best of 3: 35.99 minutes in California, but didn't come close to that time for the rest of the season. Nevertheless, he was British runner-up in July and also took part in World Championships for the first time a month later . He came his lead on a time of 3: 47.30 minutes, with which he was eliminated. Overall, he finished 34th in his first international adult championships. In 2018 he was able to slightly improve his best time in the same place as a year before. In the spring of 2019, Kerr first improved to a hall time of 3: 35.72 minutes and thus set a new British U23 record. During the summer season he was able to improve his time to 3: 33.60 min in June and thus set a new British U23 record. After he was again British runner-up in August, he went to the World Championships in Doha in October . He continuously increased his times from the preliminary to the final run, in which he set a new personal best with 3: 32.52 minutes. Overall, he ended up in sixth place with this time. Kerr, who starts for Edinburgh AC, joined the Brooks Running team in the United States, under coach Danny Mackey.