Rudolf J. Heinemann studied art history in Munich and Florence, and at the Kaiser Friedrich Museum in Berlin. He began his work in art as an apprentice to his father, who was an art dealer in Munich, the E.A. Fleischmann's Hofkunsthandlung, later Galerie Fleischmann. When his father died in the late 1920s Rudolf took over the direction of the gallery. He left Europe for the United States in 1935, bringing most of his personal art collection with him, and became a naturalized U.S. citizen in 1941. He continued to act as an international art dealer, and he was instrumental in obtaining for the 1939 San Francisco World's Fair a loan exhibition of Italian art treasures. He helped develop the Thyssen Museum in Lugano, Switzerland, and in obtaining some of its greatest paintings. He had by the time of his death completed the editing of a two-volume revision of the Thyssen catalogue of its paintings. He died in February 1975, at the age of 73, and was survived by his widow, Lore Heinemann.
Heinemann also traded under the name "Pinakos, Inc." the 1940's and 1950's, and worked extensively on joint account with Knoedler's. Heinemann would often acquire paintings in Europe for Knoedler to sell from their New York office.