James Alexander MacNabb (26 December 1901 – 6 April 1990) was a British rower who competed in the 1924 Summer Olympics.

At Cambridge, MacNabb, Maxwell Eley, Robert Morrison and Terence Sanders, who had rowed together at Eton, made up the coxless four that in 1922 at Henley won the Stewards' Challenge Cup as Eton Vikings and the Visitors' Challenge Cup as Third Trinity Boat Club.

MacNabb rowed for Cambridge in the Boat Race in 1924,[2] and also won Silver Goblets at Henley in 1924 partnering Maxwell Eley.

[3] The coxless four crew won Stewards' at Henley again in 1924 and went on to win the gold medal for Great Britain rowing at the 1924 Summer Olympics.

MacNabb served in World War II in the Royal Artillery in West Africa and Burma.