Art historian Paul Crossley described him as "the most prolific and arguably the most influential writer on Gothic architecture in the post-war years".

In 1942 his application, as a conscientious objector, for exemption from military service having been denied, he refused to submit to a medical examination, as a necessary preliminary to call-up, and was sentenced to 12 months' imprisonment.

[8] He had begun to publish articles on medieval architecture in 1936, and his prodigious stream of publications, including numerous books, continued in the post-war years.

His magisterial biographical dictionary of English Mediaeval Architects, the first edition of which appeared in 1954, contained 1,300 entries, and has been described as "a feat of titanic proportions".

[11] Paul Crossley considers that "his Neo-Romantic sensibilities propelled him beyond romanticism into real historical understanding, inspired by a tenacious curiosity for fact, and based on a phenomenal learning".

[12] Elsewhere, Crossley compares Harvey's Gothic World (1950) with Nikolaus Pevsner's Outline of European Architecture (1942) and finds that the contrast "could not have been more telling: Harvey patiently accumulating masses of detailed research to fill his survey with lists of empirical data, Pevsner subsuming detail into the broad sweep of a pan-European synthesis".

[14] In 1963 Harvey moved to York, where he was employed until 1970 as an investigator and editor (again on a part-time basis) by the Royal Commission on the Historical Monuments of England.

[2] Harvey's conviction of the importance and uniqueness of the English Gothic style meant that in much of his writing, in Crossley's view, "his nationalism continued to distort his judgement".

[2] For his 70th birthday in 1981, rather than presenting him with the customary scholarly Festschrift, Harvey's friends and admirers helped fund the second edition of his English Mediaeval Architects (published 1984; further revised 1987).