An expert on Picasso, Degas, and others, he held one of the most significant collections of twentieth century masters during his years operating the Stephen Hahn Gallery in New York City.
[2][3] Hahn began his career as a New York art dealer buying and selling paintings from the trunk of his car.
[2] An early champion of Jean Dubuffet, he eventually opened the Stephen Hahn Gallery at 75th Street and Madison Avenue.
The Camille Pissarro painting, "Rue St. Honoré, après midi, effet de pluie" which is disputed in the Cassirer v Thyssen case, was purchased in October 1976 by Baron Hans Heinrich Thyssen-Bornemisza from the Stephen Hahn Gallery after passing through the dealers Frank Perls and Knoedler.
[6][7] In another case, Picasso's “Femme en Blanc” (Woman in White) was purchased by Marilynn Alsdorf and her late husband, James from Stephen Hahn.