Alastair Chalmers OLY (born 31 March 2000) is a British track and field hurdler who specialises in the 400 metres hurdles.

He won Guernsey's first-ever Commonwealth Games track and field medal when he took bronze at the 2022 edition and he is a five-time British 400m hurdles champion.

[9] On 6 August 2022, he won the first-ever track and field medal for Guernsey in the history of the Commonwealth Games when he claimed bronze at the 22nd edition of the event in Birmingham, England.

[10][11][12] In July 2023, Chalmers took more than half a second off the championship record to win the 400m hurdles at the Island Games held in Guernsey.

[13][14] He went on to win a second gold of the event in the 4x400 metres relay with the Guernsey team setting another Games record in the process.