Banastre Tarleton (1754-1833) was perhaps the most reviled British officer to have fought against American forces during the Revolutionary War; he remains the most infamous character in the popular literature and mythology of that conflict. A recent biography examining the origins of his eventual reputation in light of historical fact reveals that it was more often the product of rebel propaganda and the contemporary need for a Tory villain than is proved by the actual record of his truly extraordinary military prowess and (usually) gentlemanly restraint; see Anthony Scotti, Brutal Virtue (Bowie, MD, 2002).
The reverse of the miniature is engraved "Colonel Turleton". A search of contemporary annual British Army Lists indicates there was no officer by the name of Turleton in the British army in the late 18th century. However, one finds both Banastre Tarleton's names frequently spelled phonetically by his contemporaries in different ways, so this spelling is not surprising. Two known post-war portraits of Tarleton display a notably similar physiognomy to that presented in this miniature - an engraving after Blackberd published in 1799 and a watercolor by his wife, Lady Tarleton, both viewable on a website devoted to Banastre Tarleton: http://www.banastretarleton.org.
The key identifying feature in terms of date, and thus origin, however, is the uniform depicted here, which is that of a specific rank - Brigade Major to a Cavalry Brigade. This was a unique staff appointment distinguished by a particular uniform - precisely as presented in this miniature. Embroidered loops of this design denote Staff, silver loops in pairs signify a Brigade Major, and the epaulette being placed on the left indicates cavalry. While Tarleton was recorded in General Orders as the Brigade Major to the cavalry brigade under General Clinton from February 7, 1778 until his appointment on the August 1, 1778 as Lt. Colonel of the British Legion (wearing their distinctive green uniform), a number of sources also point out that he was made a Major of Brigade from January of 1777 in a separate appointment, probably in recognition of his capture of General Charles Lee in December 1776. The depiction of Tarleton wearing this Staff uniform effectively dates the miniature between around January 1777 and August 1778. For more information on British uniforms, see N. P. Dawnay, "The Staff Uniform of the British Army, 1767-1855," Journal of the Society for Army Historical Research XXXI (1953), pp. 64-84, 96-109.
Tarleton was active in the New York New Jersey area from the autumn of 1776, and was then with the troops occupying Philadelphia from September 26, 1777 until June 1778, when he returned with the army to New York. By early fall, 1779, Tarleton and the British Army headed south. He returned to England in 1782.
The linear hatching of the background of the miniature, as well as the handling of the uniform and the pale features are finely executed, indicating that it was painted by a skilled miniaturist. There were relatively few painters living and working in either Philadelphia or New York during the period when this miniature was most likely painted; those known to have painted miniature portraits of British officers include Charles Willson Peale (1741-1827), James Peale (1749-1831), Pierre Eugene Du Simitiere (1737-1784), John Ramage (1748-1802) and possibly Matthew Pratt (1734-1804).