Augustine "Austin" Colin Macdonald, youngest child of Hugh Macdonald (1788-1857) and Catherine Kennedy Macdonald (ca. 1795-1872), was born 20 June 1837 in Panmure Island, Prince Edward Island. He married Mary Elizabeth MacDonald (16 February 1840 - 1 February 1918) on 27 June 1865. They had seven children: M. Josephine (b. 1867), W. Jane (b. 1869), S. Francis (b. 2 July 1871), C. Helena (b. 2 May 1874), A. Florence (b. 1878), A. J. Louis (b. 1880), and A. Ernest (b. 17 February 1883). Daughter Josephine married Roderick James Macdonald.

Austin was involved in the firm of A. A. Macdonald and Bros. with his brothers Andrew Archibald and Archibald John and engaged in a range of business activities through the family business. He was also involved in local politics, representing the 3rd district of Kings County in the Legislative Assembly as a Conservative from 1879 to 1873. Austin was a Member of Parliament for Kings County from 1873 to 1874, 1878 to 1886, and 1892 to 1896. He was appointed Lieutenant Governor of Prince Edward Island in 1915. Austin died in office on 16 July 1919.