Donald Alexander MacKinnon (22 February 1863 – 20 April 1928) was a Canadian teacher, lawyer, politician, author, and the eighth Lieutenant Governor of Prince Edward Island from 1904 to 1910.

He later received a first-class teaching licence from the Prince of Wales College in Charlottetown.

He opened a practice in Georgetown, Prince Edward Island in 1887 where he remained until moving to Charlottetown in 1897.

From 1893 to 1900, he was a member of the Legislative Assembly of Prince Edward Island for the electoral district of 4th Kings.

In 1899, he was chosen as attorney general in the cabinet of Donald Farquharson; however, as a result of the appointment, he was required to run for reelection and he was defeated.