Alastair Chalmers (born 31 March 2000) is a British track and field hurdler who specialises in the 400 metres hurdles. The Guernsey record-holder for the 400 metres hurdles, Chalmers currently competes for both Guernsey and Great Britain. In addition to multiple Island Games medals, Chalmers is the 2017 Commonwealth Youth Champion. In 2022 Chalmers became British 400m Hurdles Champion for the third successive year.