Cameron Chalmers gained his first international experience in 2016, when he reached the semi-finals at the U20 World Championships in Bydgoszcz , where he was eliminated with 46.51 seconds. The following year he reached fourth place in the U23 European Championships there in 46.29 seconds and won the British 4 x 400 meter relay in 3: 03.65 minutes. In 2018 he took part for Guernsey in the Commonwealth Games in the Australian Gold Coast and was eliminated there with 46.34 s in the semi-finals. In the summer he was given a starting place in the relay for the European Championships in Berlin , where he contributed to winning the silver medal behind Belgium. In 2019 he reached the semi-finals in the individual competition at the European Indoor Championships in Glasgow , where he was eliminated with 47.83 seconds, while he finished fifth in the relay in 3: 08.48 minutes. He also finished fifth at the World Relays in Yokohama after 3: 04.96 minutes and then won the silver medal behind Frenchman Fabrisio Saïdy in 45.92 seconds at the U23 European Championships in Gävle and also won the relay in 3: 04.59 min the silver medal behind Germany. With the British relay he also took part in the World Championships in Doha and also reached the final there , in which the team did not reach the finish line.
In 2019 Chalmers became British indoor champion in the 400-meter run. He is a student at the University of Bath . His younger brother Alastair Chalmers is also active as a track and field athlete.