Kahanamoku easily qualified for the U.S. Olympic swimming team in 1912, breaking the record for the 200 meter freestyle in his trial heat for the 4×200 relay. He went on to win a gold medal in the 100 yard (91 m) freestyle in the 1912 Olympics in Stockholm, and a silver with the relay team. During the 1920 Olympics in Antwerp, he won gold medals both in the 100 yd (91 m), bettering fellow Hawaiian Pua Kealoha, and in the relay. He finished the 100 yd (91 m) with a silver medal during the 1924 Olympics in Paris, the gold going to Johnny Weissmuller and the bronze to Duke's brother, Samuel Kahanamoku. Duke Kahanamoku was the first person to be inducted into both the Swimming Hall of Fame and the Surfing Hall of Fame. The Duke Kahanamoku Invitational Surfing Championships are named in his honor. He served as sheriff of Honolulu, Hawaii from 1932 to 1961.