Susan Agnes Bernard Macdonald (August 24, 1836 – May 9, 1920) was the second wife of Sir John A. Macdonald, the first Prime Minister of Canada. She also carried the title Baroness Macdonald of Earnscliffe. She was born in Jamaica.

Married on February 16, 1867, they had one daughter, Margaret Mary Theodora Macdonald (1869-1933).

Known as Agnes, she died in England and was buried in the Ocklynge Cemetery in Eastbourne, a city just south of London.

See also: Spouses of the Prime Ministers of Canada.