Mr Chalmers picked up the bronze medal in the race, completing it in 49.97 seconds on Saturday during the Birmingham 2022 Games.
He won the medal in front of 30,000 spectators inside the Alexander Stadium.
Mr Chalmers said he was proud to have put Guernsey on the map.
COMMONWEALTH GAMES ????Absolutely unbelievable moment and I just want to thank everyone for the support‼️LETS GOOOOOO???????????????????????????????????? https://t.co/UXuzysJcMh
— Alastair Chalmers (@GsyAla) August 6, 2022
Watch: Mr Chalmers on the final straight and crossing the line.
Deputy Peter Ferbrache, President of the Policy & Resources Committee, said the whole island is proud of his accomplishment.
“I am old enough to remember the exploits of David Hemery in the 400m hurdles in Mexico, so I find it memorable that our Alastair Chalmers, in the same iconic event, won his magnificent bronze medal at the Commonwealth Games,” he said.
“Truly fantastic. What an athlete, what an achievement, we are so proud of him.”
Boxer Billy Le Poullain will be the flagbearer for Team Guernsey at tonight’s closing ceremony.
Guernsey’s remaining athletes are returning to the island tomorrow morning.
Moments to cherish ????
Incredible highlights captured from last night at the Commonwealth Games in Birmingham ????#B2022 #WhereItStarts pic.twitter.com/p3W6I6CSL8
— British Athletics (@BritAthletics) August 7, 2022
Pictured: Mr Chalmer’s achievement was noted by British Athletics.