Robert D. Sack has, since August 6, 1998, been a Judge of the United States Court of Appeals for the Second Circuit with his chambers at 40 Foley Square.

During his 33 years in practice, he specialized in national and international press law. He was a frequent lecturer and writer on press law topics and is the author of Sack On Defamation: Libel, Slander, And Related Problems. On May 1, 2008, Judge Sack was awarded the Federal Bar Council's Learned Hand Medal for excellence in federal jurisprudence.

Judge Sack was an officer and director of the William F. Kerby and Robert S. Potter Fund, which assisted in funding the legal defense of journalists abroad, and a member of the advisory boards of the Bureau of National Affairs' Media Law Reporter and the ABA Forum Committee's Communications Lawyer. He is a member of the Board of Visitors of the Columbia Law School and was a member of the Board of Trustees of Columbia University Seminars on Media and Society. He has, since 2001, been an Adjunct Professor of Law at Columbia Law School.