As Deputy Director for Grants and Publications, Martin is responsible for the direction of the Centre's Grants and Fellowship programme, its publication schedule and its Yale-in-London teaching programme.

Martin joined the Centre in 2007 as Assistant Director for Academic Activities, later Deputy Director of Studies, then Deputy Director for Collections & Publications. Between 1998 and 2007 he worked at Tate Gallery as Senior Curator, and was subsequently appointed Head of British Art to 1900. From 1992 to 1998 he was Director of the London Centre of the University of Delaware and Associate Professor of Art History.

Martin holds a PhD from Birkbeck College, University of London, an MA in British Romantic Art from the Courtauld Institute of Art, University of London, and a BA in Art History with History from the University of Nottingham. He is also a Fellow of Society of Antiquaries. Martin's research interests focus on eighteenth- and nineteenth-century British Art, including portraiture, landscape and the history of art academies.

Martin’s publications include Sir Joshua Reynolds: The Subject Pictures (Cambridge University Press 1995), Gainsborough (Tate and Princeton University Press 2002), and, with David Mannings, Sir Joshua Reynolds: A Complete Catalogue of his Paintings (Yale University Press 2000). Among the exhibitions he has curated are The Artist's Model: Its role in British Art from Lely to Etty (Kenwood and Nottingham 1991, with Ilaria Bignamini), Angels and Urchins: The Fancy Picture in 18th-Century British Art (Kenwood and Nottingham 1998), The Artist's Model: From Etty to Spencer (Kenwood, Nottingham and York 1999, with William Vaughan), Art of the Garden: The Garden in British Art, 1800 to the Present Day (Tate Britain, Belfast and Manchester 2004, with Nicholas Alfrey and Stephen Daniels), Joshua Reynolds: The Creation of Celebrity (Tate Britain and Palazzo dei Diamanti, Ferrara 2005), Stanley Spencer and the English Garden (Compton Verney, (Compton Verney 2011, with Steven Parissien), Johan Zoffany, RA: Society Observed (Yale Center for British Art and the Royal Academy of Arts, London 2011–2012), and Richard Wilson and the Transformation of European Landscape Painting (Yale Center for British Art and the National Museum Wales, Cardiff, 2014).

Martin is currently leading the Paul Mellon Centre’s research project, Collecting and Display in the British Country House, which is to be published online by the Centre in 2020. He is also the co-curator of George Stubbs: "All done from Nature" at the MK Gallery, Milton Keynes, 12 October 2019 to 26 January 2020.