Mahoney joined Latham & Watkins in 1980 and remained at the firm for the next 11 years. She then served as Deputy Solicitor General in the George H. W. Bush administration, where she was a colleague of future Chief Justice of the United States John G. Roberts. In April 1992, President George H. W. Bush nominated her to serve as a judge of the United States District Court for the Eastern District of Virginia, but her nomination was not acted upon by the Senate before Bush's presidency ended. "It was definitely the low point of my career," she has said. "I never had a hearing, and there was never any opposition that I knew of, so it wasn't ugly. It was just disappointing."