Arbuthnot joined the Royal Navy about 1727. The short biographical sketch in the DCB points out that his promotion was slow, "becoming a lieutenant in 1739, a commander in 1746, and a post-captain in 1747. Arbuthnot was, in November of 1759, with Hawke at Quiberon Bay as the captain of the 50 gun Portland, a second rate ship. He then saw service in the last battle of the Seven Years War at Havana.1
Arbuthnot, "after a period of command at Portsmouth" was appointed to command the Naval Dockyard at Halifax, arriving there in November of 1775. A few months later, in April of 1776, caught short because they were obliged to order Governor Legge back to England to answer charges, Arbuthnot was, by those in power at London, appointed the Lieutenant-Governor of Nova Scotia; this, at a very important time when the American colonies were in revolt. In January of 1778, Arbuthnot was recalled and at the same time promoted to Rear Admiral. In 1779 he was appointed commander of the Atlantic Station and as such was to see action in the war against the colonies. In one, the 1779 siege on Charleston, South Carolina, he was to receive praise; in another, the 1781 fight with the French fleet in Chesapeake Bay, he was to be criticized. He was recalled after the Chesapeake Bay fight, in 1781; and, then being seventy years old he pretty much went into retirement, though in 1793, in virtue of his seniority he was appointed Admiral of the Blue. Overall history has not been too kind to Mariot Arbuthnot; we read from the Dictionary of National Biography that one, "can hardly tell what principles he is of, besides of a blustering Tar. It seems he certainly suffered from chronic absentmindedness.2 To quote Brebner, Arbuthnot was "a gullible, affable person who never seemed to learn from his mistakes."3
 Kempt, Oxford Companion to Ships and Sea.
 See, "The Error of Marriot Arbuthnot" by Clarke, NSHR, #8:2(1988).
 See, The Neutral Yankees, Fn at p. 296.