After graduation, Summerson worked in several junior roles, most notably in the office of
Sir Giles Gilbert Scott, but architectural practice was not for him and he became a tutor at the
Edinburgh College of Art, School of Architecture in 1929. Hired by the
Modern Architectural Research Group (MARS), a think tank founded by a group of modernist architects, he settled back in London, moving on to a job as an assistant editor for the magazine
Architect and Building News in 1934. His
Architecture in Britain: 1530–1830 (1st edition 1953; many subsequent editions) remained a standard work on the subject for students and general readers after his death.
The Classical Language of Architecture (1963) is an introduction to the stylistic elements of classical architecture and traces their use and variation in different eras. He also wrote many more specialised works, including books about
Inigo Jones and
Georgian London (1945) illustrated by
Alison Sleigh, as well as
The Architecture of the Eighteenth Century (1986), in which he describes
Boullée in a distinct positive manner, stating that Boullée was clearly the point of departure for one of the boldest innovators of the century,
Claude Nicolas Ledoux. His 1945 book
Georgian London was called "a masterpiece of British art history" by
Simon Jenkins in a
Sunday Times review of the 1988 edition. One of the founders of the
National Buildings Record (NBR) in 1941, Summerson served as its deputy director yet also took to the streets taking photographs for the organisation. He sat on many other public bodies and committees, including the
Royal Fine Arts Commission (1947–54) and the
Historic Buildings Council (1953–78) In 1945, Summerson was appointed Director and curator of
Sir John Soane's Museum, a post he held until his retirement in 1984. and Slade Professor at
Cambridge University for the 1966–7 academic year. He gave the 1964 Master-Mind Lecture on
Inigo Jones. Summerson lectured at
The Courtauld Institute of Art on the history of Georgian architecture in London, Summerson was noted for his somewhat elitist approach, and he was not always a consistent friend of the conservation movement. He was hired by the
ESB in Ireland to speak in favour of their demolition of 16 Georgian townhouses in Fitzwilliam Street,
Dublin. The doomed terrace, he said, was "simply one damned house after another". ==Honours==