Robert J. D. Harding joined Maggs Bros as an assistant to Bryan Maggs on a school holiday job at Easter 1976. Since then, he has specialised in Medieval and Early Modern British printed books, manuscripts, and bindings with a particular interest in the history of collecting, as exemplified in the series of Books & Readers in Early Modern Britain catalogues. He worked closely with Bryan Maggs on developing and curating the Wormsley Library for Sir Paul Getty and succeeded Bryan as part-time librarian there in 2023.

He has contributed essays and reviews to The Antiquaries Journal, The Book Collector, The British Art Journal, Master Drawings, Poetica, Print Quarterly, The Wildean,  and most recently, The Library: Papers of the Bibliographical Society of London, has contributed two entries to the Oxford Dictionary of National Biography ('Wenceslaus Hollar' and 'Founders of the Savile Club', the latter forthcoming), an essay on Tudor bookbinding to a volume of papers on Tudor Books and Readers (the result of a 2011 conference at the Huntington Library in California), individual entries to group books on the Treasures of Cambridge University Library and Lambeth Palace Library and was a major contributor to the catalogue of The Wormsley Library: a personal selection by Sir Paul Getty, K.B.E. exhibition at the Morgan Library in New York in 1999. He has also compiled two volumes devoted to the Savile Club members and staff who gave their lives in the First and Second World Wars (2018 and 2023).

He is a Fellow of the Society of Antiquaries and a Liveryman of the Company of Stationers, was a committee member for nine years of The Walpole Society (a hundred-year-old charity devoted to publishing new research on British art and collecting), and was chairman of the Savile Club from 2014-21.