Stephen Ongpin has more than twenty years of experience as a dealer in Old Master and 19th century drawings. He began his career at the famous art dealership of P. & D. Colnaghi in 1986, working at the firm's New York branch for ten years before moving to London in 1996. Working closely with Jean-Luc Baroni in the drawings department of Colnaghi, Stephen was responsible for researching, writing, and editing the gallery's annual catalogues of Master Drawings. In 2001 he joined Baroni in forming Jean-Luc Baroni Ltd. in London, with Stephen continuing to assume responsibility for the new firm's drawing department, organizing their successful drawings exhibitions and writing the accompanying catalogues. He has to date researched and written nearly thirty scholarly catalogues of drawings.

Since late in 2006, Stephen Ongpin has worked independently as a private dealer and consultant in the field of Old and Modern master drawings. In December 2007 he opened a gallery at 6 Mason's Yard, in the heart of St. James's in London.