After a brief period at the Manchester City Art Gallery, Gibson joined the National Portrait Gallery as an assistant curator in 1968 and was almost immediately involved in the establishment of the photographic department, the role of which he would significantly develop and expand during his career.
This occasionally led him into controversy, such as when the gallery's board of trustees rejected a portrait of Alan Bennett by Tom Wood in 1992 to the embarrassment of all concerned.
In 2000 he curated 'Painting the Century: 101 Portrait Masterpieces 1900–2000', writing the book, with an introduction by Norbert Lynton that accompanied the exhibition.
He published numerous reference works on art history, including examinations of animals in portraiture and several studies of painting in the twentieth century, and contributed to the Dictionary of National Biography, Folio, The Independent, Modern Painters & the Museums Journal.
Gibson settled in Hempstead, Essex and became involved with the Fry Art Gallery.