Upon Isaacson's return to New York, he became an art dealer almost by accident, taking on Edwin Hewitt's gallery at the request of mutual friend Lincoln Kirstein. Although the Robert Isaacson Gallery, located at 22 East 66th Street, represented the estate of Elie Nadelman and championed Magic Realist painters (including his favorite, George Tooker), Isaacson's growing interest and fascination with nineteenth century academic painting, an extremely unfashionable pursuit in the 1950s, would in time make him the paradigm of the scholarly dealer: his opinions and near-encyclopedic knowledge of the once-obscure field were sought long after the Robert Isaacson Gallery shut its doors (around 1970) and Isaacson began devoting himself full-time to curating and collecting. Isaacson played an important role in helping rehabilitate the reputations of Lawrence Alma-Tadema,An Exhibition to Commemorate the 50th Anniversary of the Death of Sir Lawrence Alma-Tadema, 1836-1912. New York: Robert Isaacson Gallery, 1962. Charles Bargue, William-Adolphe Bouguereau,Isaacson, Robert. William-Adolphe Bouguereau (catalogue). New York Cultural Center and Farleigh Dickinson, 1974. Thomas Dewing, Jean-Léon Gérôme,Isaacson, Robert. Jean-Léon Gérôme and his pupils. Poughkeepsie, New York: Vassar College Art Library, 1967. Albert Joseph Moore, Mihály Munkácsy and Gaston La Touche, among others.
