Anglo-Irish architectural historian. He began work as an architect in the office of (Sir) Giles Gilbert Scott in 1926, later assisting Adrian Gilbert Scott with the working-drawings for the upper stage of the noble tower of Hansom's Church of the Holy Name, Manchester. He also worked for W. D. Caröe before becoming an architectural journalist. As assistant editor of the Architect and Building News (1834–41) he developed his cool, even icy, style of criticism, as well as cultivating his support for International Modernism (in his 1957 lecture ‘The Case for a Theory of Modern Architecture’, he made a forlorn attempt to promote a solid philosophical base for Modernism, recognizing that Classical architecture had always had just that, but his efforts in this respect remain wholly unconvincing).
He made his name with his biography of John Nash (1935, 1949, 1980), yet after the 1939–45 war argued that only a fraction of Nash's scenographic architecture around Regent's Park should be preserved (a predictable Modernist stance, despite the fact that it ceases to be scenographic if fragmented). A founder-member of the Georgian Group (1937), he was also not in favour of anything but highly selective retention of C18 and early C19 buildings. During the war he established, and was Deputy Director of, the National Buildings Record (1941–5), and made extensive photographic records of London buildings: with James Maude Richards (1907–92) he was responsible for The Bombed Buildings of Britain: A Record of Architectural Casualties 1940–41 (1942, 1947). He brought out his magisterial Georgian London (subsequently edited by Colvin and reissued 2002–3) in the year he was appointed Curator of Sir John Soane's Museum, a position he held until 1984. He wrote several perceptive essays on Soane's work, but never produced a major study, probably because he found Soane's architecture and personality uncongenial. On the other hand, he pioneered studies of John Thorpe, and, under Colvin's rigorous editorship, contributed much material on C16 and C17 architecture to the History of the King's Works (1975, 1982). In 1953 he made a valuable contribution to the Pelican History of Art series of volumes with his Architecture in Britain 1530–1830, which went into several editions: in that work his appreciation of the earlier periods (including the designs of Inigo Jones, Wren, and others) as well as his ambivalence towards figures such as Nash and Soane were made overt. His attempts to produce a Victorian sequel to Georgian London resulted in Victorian Architecture: Four Studies in Evaluation (1970), The London Building World of the Eighteen-Sixties (1973), and The Architecture of Victorian London (1976), with other articles collected as The Unromantic Castle (1990). Clearly Summerson was uncomfortable with much of Victorian architecture, finding its variety (and, one suspects, its rumbustiousness) unpalatable, but his scholarly essays on Inigo Jones, Wren, Viollet-le-Duc, and others reveal areas he found more to his taste.
Towards the end of his life he modified some of his earlier acerbic judgements, and seems to have become disillusioned with aspects of the Modern Movement. Nevertheless, he supported the demolition of Victorian fabric in the City of London to enable new buildings to go ahead, in spite of having admitted that ‘cheap modern’ was all Britain ever had (a view from which it would be hard to dissent).