After her father's death from cholera she came to Barrie, Upper Canada, with her mother in 1854 to live with her brother, Hewitt Bernard (who left in 1851 after giving up the family plantation), a lawyer and private secretary to political leader John A.

It was in 1866, in London, England, where Miss Bernard had been with her mother that she again met her husband-to-be, who was there to prepare the British North America Act.

They married on 16 February 1867, and had one daughter, Margaret Mary Theodora Macdonald (1869–1933), who was born severely handicapped, both mentally and physically.

[3] On the first prime ministerial trip to British Columbia on the newly opened Canadian Pacific Railway, Macdonald built Agnes a platform on the cowcatcher of the locomotive and had a chair nailed to it so she could better see the mountain scenery.

After her husband's death in 1891 she was raised to the peerage in his honour as Baroness Macdonald of Earnscliffe, in the Province of Ontario and Dominion of Canada.