Étienne Desmarteau (4 February 1873 – 29 October 1905) was a Canadian athlete, winner of the weight throwing event at the 1904 Summer Olympics. For some time, it was thought that Desmarteau was the first Olympic champion from Canada, but it was later discovered that 1900 champion George Orton, who ran for an American university, was also Canadian.

The Boucherville-born Desmarteau, member of the Montréal Athletic Club was one of the top competitors in the 56 lb (25.4 kg) weight throwing event, which is no longer held. In 1902 he had won the American AAU championships, beating John Flanagan . Flanagan broke the world record in the event prior to the 1904 Olympics, making him one of the favourites for the event along with Desmarteau.

To compete in the Olympics, Desmarteau, a policeman in Montréal, had to ask for a leave of absence to go to St. Louis, but he was denied by his employer. He decided to go anyway, which cost him his job. In St. Louis, his first throw was 34 ft 4 in (10.46 m), enough for victory over Flanagan, who didn't manage better than 33 ft 4 in.

He received a hero's welcome back in Montréal, but he would not enjoy his title for long. The following year, he died of typhoid fever. A park and a sports arena in Montréal have been named after him; the Aréna Étienne Desmarteau was used as a venue for basketball during the 1976 Summer Olympics.