Charles Riddy was a member of the Toronto Argonauts Rowing Club when he was selected to represent Canada in the coxed eights at the 1908 Summer Olympics. There, alongside Gordon Balfour, Becher Gale, Douglas Kertland, Walter Lewis, Irvine Robertson, Geoffrey Taylor, Julius Thomson, and Joe Wright, Sr., he was defeated in the semifinals by the eventual gold medal-winning Leander crew from Great Britain and settled for bronze. He also competed in the coxless fours, alongside Balfour, Gale, and Taylor, but was eliminated in the opening round (although for historical purposes he is considered a bronze medalist, as there were only four teams in the event). He made a second appearance with the Argonauts in the coxed eights at the 1912 Summer Olympics, but was again defeated by the Leander crew (who would go on to win the event) and eliminated from the tournament. In May 1918 his exemption from overseas service during World War I was refused, but the conflict ended before he saw any action.
Canada