Robert B. Barnett (August 26, 1946)is an American lawyer who is a partner at the law firm Williams & Connolly LLP.
Barnett was born in Waukegan, Illinois. He obtained a bachelor's degree from the University of Wisconsin in 1968 and a law degree from the University of Chicago in 1971. He was comment editor for the University of Chicago Law Review and later clerked for John Minor Wisdom and later Byron White on the Supreme Court. An aide to Walter Mondale, in 1975 he joined the law firm of Williams & Connolly.
He was ranked by Washingtonian magazine as the #1 Washington, D.C. area lawyer in 2004 and number 10 in 2007.