Upon leaving the Department of Justice in 1993, Barr was appointed by Virginia Governor George Allen to co-chair a commission to reform the criminal justice system and abolish parole in the state. Later in 1994, Barr became Executive Vice President and General Counsel of GTE Corporation, where he served for 14 years. During his corporate tenure, Barr directed a successful litigation campaign by the local telephone industry to achieve deregulation by scuttling a series of FCC rules, personally arguing several cases in the federal courts of appeals and the Supreme Court. In 2000, when GTE merged with Bell Atlantic to become Verizon Communications, he left that position. While at GTE, from 1997 to 2000, Barr also served on the Board of Visitors of the College of William & Mary.

In 2009, Barr was briefly of counsel to the firm Kirkland & Ellis. From 2010 until 2017, he advised corporations on government enforcement matters and regulatory litigation; he rejoined Kirkland and Ellis in 2017.