 In 1937, he completed a gilded bronze equestrian statue of Anthony Wayne for the Philadelphia Museum of Art.Gregory is well known for his architectural sculpture.Examples include bas relief panels on the structure and sarcophagus of the Huntington Mausoleum by architect John Russell Pope at The Huntington Library in San Marino, California; and the larger-than-life panels, "Columbia" and "Urban Life", on either side of the steps in John Marshall Park, Judiciary Square, Washington, D.C.

Gregory was a member of the National Sculpture Society, the American Federation of Arts, and the Beaux-Arts Institute of Design.