Baillie, William (1723–1810), printmaker and art dealer, was born 11 June 1723 at Kilbride, Co. Carlow, the second son of the upholsterer Robert Baillie of Celbridge, Co. Kildare, and his wife Susanna (née Antrobus). After his education at Dr Thomas Sheridan's (qv) school in Dublin, he attended TCD, before entering the Middle Temple, London (10 May 1742). Quickly exchanging a prospective legal career for a commission as ensign in the British army in June 1744, he served under the duke of Cumberland at Culloden (1746) and under the marquis of Granby in Germany. Baillie rose to the rank of captain, before poor health induced his retirement in 1761, and he later held the position of commissioner of stamps (1773–1795). He had two sons and two daughters with his wife, Elizabeth.
Baillie's military career overlapped – and occasionally inspired – his lifelong passion for art, and he is now chiefly remembered as an accomplished engraver. It is uncertain if he received artistic training, though an inscription on an undated print acknowledges instruction from Nathaniel Hone (qv) the Elder (d.1784), with whom he associated in London. Baillie's earliest known print is a portrait of John Golding (1753), and he occasionally produced military-themed prints etched from his own original paintings. More typically, however, he reproduced the work of seventeenth-century Dutch and Flemish masters in his own or aristocratic collections, specialising in Rembrandt van Rijn. He owned three of Rembrandt's plates, including the celebrated ‘Christ healing the sick’ (1649), also known as ‘The hundred guilder print’, which he restored and reworked in 1775. Several different impressions from this plate were exhibited at the Society of Artists in London (1776), where he was an honorary exhibitor (1772–1776) and elected an honorary fellow. In all he produced over a hundred prints, and his work proved enduringly popular; collected sets of his prints were sold by Walter Shropshire (between 1773–1776), and subsequently by Boydell in 1792 (2 vols, reissued 1803 and 1807).
Baillie's proficiency in engraving fostered an adjacent career as art connoisseur and advisor to the aristocracy (often in conjunction with Hone). He is caricatured in James Gillray's engraving ‘Connoisseurs examining a collection of George Morlands', (1807; National Portrait Gallery, London). He travelled to The Hague in 1763 to buy paintings for James Lowther, 1st earl of Lonsdale, and was instrumental in forming the collection of John Stuart, 3rd earl of Bute. He died 22 December 1810 at his home in Paddington, London. Three likenesses of Baillie are in the National Portrait Gallery, London.