Harold Hackett (July 12, 1878-November 20, 1937) was an American tennis player.
Born in Hingham, Massachusetts, but a long-time resident of New York, Hackett turned in his best results in doubles with Fred Alexander. Beginning in 1905, they were finalists at the U.S. Nationals a record seven consecutive years, winning in 1907, 1908, 1909, and 1910.
A graduate of Yale University, Hackett and Princeton University graduate Alexander won the U.S. Indoor doubles three times (1906-08), and he teamed with Walter Hall to win the U.S. Clay Court doubles title in 1912.
The following year, 1913, he was player-captain of the U.S. Davis Cup team that beat the United Kingdom in the final to win the Cup.
Hackett was ranked in the U.S. Top Ten twice: in 1902 and at number seven in 1906 (when he was a U.S. quarterfinalist). He was inducted into the International Tennis Hall of Fame in 1961.