Clark was elected a member or honorary member of the Conseil Artistique des Musées Nationaux of France; the American Academy of Arts and Sciences; the American Institute of Architects. the Swedish Academy; the Spanish Academy; the Florentine Academy; the Académie française; and the Institut de France. He was awarded honorary degrees by the universities of Bath, Cambridge, Glasgow, Liverpool, London, Oxford, Sheffield, Warwick, York, and in the US Columbia and Brown universities. He was an honorary fellow of the Royal Institute of British Architects and the Royal College of Art. Other honours and awards included Serena Medal of the British Academy (for Italian Studies); the Gold Medal and Citation of Honour of New York University; and the US National Gallery of Art Medal.