His entries for the Wallace Collection's new catalogue and articles for The Burlington Magazine so impressed the administration of the Isabella Stewart Gardner Museum in Boston, Massachusetts that the trustees of the museum agreed to fund Hendy's three-year stay in Italy, during which he compiled the Gardner catalogue.
In 1933, he resigned from the Museum of Fine Arts after a quarrel with the trustees who disapproved of his purchase of Matisse's 1903 nude Carmelina.
The threat posed to Leeds during the Second World War caused the gallery's works of art to be evacuated to a more rural setting in Temple Newsam House.
The task of relocation, and the subsequent rehanging of the paintings in their new 18th-century surroundings, was undertaken by Hendy, whose work there caught the attention of the Director of the National Gallery, Kenneth Clark.
Clark, who had similarly overseen the removal of the National Gallery pictures to safety in a North Wales quarry during the war years, appointed Hendy as his successor in 1946.