Appointed as Chief Librarian in Ipswich, Suffolk in 1924, he was involved in planning the interior of the new central library there and making much of it open access, restocking the book shelves, creating a children's collection, promoting musicals, drama and other extension activities, and actively publicising the library service.
[3] In those efforts he was supported by the generosity of Bill Paul, the head of the local firm of corn merchants, R. & W. Paul Ltd.[6] During his years in Wigan and Ipswich McColvin began his long writing career, with books published including The Theory of Book Selection for Public Libraries (1927) and Library Extension Work and Publicity (1925).
[7] In 1931 McColvin was made Borough Librarian at Hampstead in North London and the curator of the Keats House Museum.
[11] He published a number of "influential" books on topics including public libraries and music librarianship.
[3] In 1938 McColvin was appointed as Librarian of the City of Westminster in central London, a position he held until his retirement in 1961.
When the Second World War broke out, he spent much time on civil defense duties and was appointed Officer-in-Charge of the City Hall Report Centre in Westminster.
Often dubbed the McColvin Report, its advocacy of its modern goals, including careful planning, benchmarking and budgeting, and improved library standards and service, along with a higher professional status for librarians and better library education, was, however, countered by "parochialism" and "conservatism" among British librarians which were only defeated after thirty years of debate and with changes in local government in the 1960s and 1970s.
[20] He was vice-president and chairman of the public libraries section of the International Federation of Library Associations (IFLA), a member of the International Federation for Information (also known by its original French name, the Fédération internationale de documentation, or FID), and a member of the British co-operating committee of UNESCO.
[3] The Library Association's and now the Chartered Institute of Library and Information Professionals (CILIP)'s ISG (Information Services Group) Besterman/McColvin Awards (often referred to as the Besterman/McColvin Medals) which originally were "for outstanding works of reference" and now are for "outstanding works of electronic resources and e-books", were named for both men.
[22] After being forced to retire in 1961 following two strokes, McColvin died on 16 January 1976 at Southgate, a suburban area of north London.