Sung is a partner in the Washington, D.C., office of the international law firm of Dewey & LeBoeuf LLP. He is a registered patent attorney specializing in biotechnology, medical device, and pharmaceutical patent litigation and counseling. He is also a law school professor and director of the Intellectual Property Law Program at the University of Maryland School of Law.

Sung is a former judicial clerk for (now Senior) Circuit Judge Raymond C. Clevenger, III, of the U.S. Court of Appeals for the Federal Circuit. He has testified before the U.S. House of Representatives Subcommittee on Courts, the Internet, and Intellectual Property regarding gene patenting, and before the U.S. Department of Justice and Federal Trade Commission Joint Hearings on Competition and Intellectual Property Law and Policy in the Knowledge-Based Economy regarding patent law and biotechnology patent pools. He has also served as a consultant to the National Human Genome Research Institute and as chair of the National Research Council Committee on Intellectual Property Concerns for Toxicogenomics. He is an accomplished author of books on patent law and numerous articles on intellectual property, biotechnology, and technology transfer.