As a young man, Daniel travelled abroad studying the attribution of paintings with Roger Fry. He was appointed as a Trustee of the National Gallery in 1925, apparently due to his being a personal friend and golfing partner of the prime minister, Stanley Baldwin. His installation as Director in January 1929 is seen as a strike against "experts" and the increasing professionalisation of art history, on the part of the Trustees.
In 1929, the Gallery bought the Wilton Diptych and Titian's group portrait of The Vendramin Family; these are considered the two major purchases of Daniel's directorship. Also that year the highly controversial dealer Joseph Duveen became a Trustee. Jonathan Conlin's history of the National Gallery describes Daniel as a "self-effacing nonentity" but Fry, for one, admired his "terrific energy and intellectual beefiness". Like many directors of the National Gallery, he was a trustee of the Iveagh Bequest.