Thomas Agnew & Sons

As The Times noted in Sir William's obituary, "in 1877 the firm had built rooms in 39 Old Bond Street (later called 43 Old Bond Street), and when the succession of Old Master exhibitions, the example of Sir Richard Wallace and the Rothschilds, and the revived passion for eighteenth-century architecture and furniture had turned the taste of the new rich men back to the older art, William Agnew was ready to find the pictures."

Consequently, in Bond Street, Agnew's enjoyed friendly relations with Knoedler, Arthur Joseph Sulley (1853–1930), the Wertheimer brothers, and in Paris, Charles Sedelmeyer (1837–1925).

The firm has handled major pictures by, amongst others, Caravaggio, John Constable, Van Dyck, El Greco, Guercino, Frans Hals, Poussin, Rembrandt, Rubens, Vermeer, Titian, Pontormo,[5] J. M. W. Turner, Joseph Wright of Derby, and Velázquez, including the latter's Rokeby Venus in the National Gallery, London.

In recent years, the gallery has increasingly promoted the establishment of lesser-known artists of the early twentieth century, namely the German-Swedish painter and portraitist Lotte Laserstein.

In 2013, after nearly two centuries of family ownership, the firm was purchased privately and the new gallery relocated its premises from Albemarle Street to 6 St James's Place, London, under the directorship of art historian Lord Anthony Crichton-Stuart.

[4] In 2021, the gallery ran an exhibition dedicated to Albrecht Dürer which included a newly found drawing by the artist: this previously unknown work has been subject to significant publicity.