Les Boardman was not among the original selections for the Australasian 1912 Olympic team, but when Edgar Findlay dropped out due to a lack of funds, Boardman assumed his position by winning a special 220 yds test race. Boardman was a teammate of Harold Hardwick and Cecil Healy at the Sydney Swimming Club and also served as captain of the club in 1912 on their trip to New Zealand to race against the Waitemata Club. At Stockholm, Boardman was eliminated in the second round of the 100 m freestyle and after Bill Longworth was unable to compete in the 4x200 freestyle relay due to an ear injury, Boardman replaced him, swimming the third leg and winning a gold medal with world records of 10:14.0, set in round one, and 10:11.2 in the final.
Boardman began competitive swimming early in life at the Cleveland-street Superior Public School, and as a junior, he was with North Sydney Club and Drummoyne Club. After joining Sydney Swimming Club, he won the club 100 yds championships in 1908 against Hardwick and also won the club’s diving championships many times. Boardman played water polo with Sydney Swimming Club. He never placed at the Australian championships, but was the New South Wales 500 yds freestyle team champion in 1914 and 1915 and Tasmanian 100 yds and 440 yds freestyle champion in 1911.