William Thuillier has built up his expertise in the area of old master paintings. Over the last few years he has successfully unearthed and sold works by Sir Joshua Reynolds, Joseph Wright of Derby, Jacopo Amigoni, John Wootton, Alessandro Magnasco and many other painters. Some of these have resulted in sales to museums, such as the National Maritime Museum Greenwich,the National Portrait Gallery, and Tate Britain , London.
As an agent he has advised clients on the disposal of important works, such as a major double portrait by Sir Peter Lely, and works by Jean-Baptiste Pater and Hubert Robert.
He has participated in several international art fairs in Tokyo, New York, Dallas and Monte Carlo, and is a regular exhibitor at the Olympia Fine Art and Antiques Fair, London, where he sits on the advisory board.