Admiral Thomas Mackenzie (1753 – 20 September 1813) was a prominent British Royal Navy officer of the late eighteenth century. Mackenzie's career, while successful, was blighted by a series of controversies that limited his opportunities and command, resulting in his placement in reserve for the last 19 years of his career. During his early service, Mackenzie served at a number of engagements in the American Revolutionary War and advanced rapidly, but he was caught during service in the Indian Ocean in the midst of a disagreement between two senior officers and as a result was placed in reserve at the end of the war. At the start of the French Revolutionary Wars ten years later Mackenzie was restored to service, and commanded the ship of the line HMS Gibraltar at the Glorious First of June