Donald MacNeil Fairfax (March 10, 1818 – January 10, 1894) was an officer in the United States Navy during the American Civil War.

His younger brother, Edwin Cary Fairfax (1833-1912), also served in the Union Army, enlisting in the 5th Pennsylvania Cavalry, Company D. As executive officer in San Jacinto, he was a participant in the 1861 "Trent Affair," a diplomatic controversy involving the U.S. Navy's removal of Confederate commissioners from the British mail-steamer, RMS Trent.

On November 8, 1861, Fairfax boarded Trent to remove Confederate commissioners James M. Mason and John Slidell, after the ship had been stopped by his captain, Charles Wilkes.

Wilkes had given Fairfax the following written instructions: On boarding her you will demand the papers of the steamer, her clearance from Havana, with the list of passengers and crew.

[3] Fairfax's distinguished service in the Civil War included command of the Cayuga, Nantucket and Montauk.