In late 1865, he moved to New York City, where he resumed the practice of law with Judge Thomas W. Bartley, former Justice of the Ohio Supreme Court and governor of Ohio, until 1869. Following his practice in New York, Burnett and his second wife moved back to Ohio, where he then practiced law with Jacob Dolson Cox, another former governor, and John F. Follett, who later served as a U.S. Representative, until 1872, when he started a practice in New York with Edwin W. Stoughton.