William Barr (born 1950) is an American lawyer and government official.
William Barr may also refer to: William G. Barr (1920–1987), Illinois state representative and businessman William Barr (historian) (born 1940), Scottish historian at the University of Calgary, Canada William Barr (artist) (1867–1933), Scottish / Californian artist Billy Barr (footballer) (born 1969), English footballer and coach Billy Barr (naturalist), American amateur scientist, known for collecting climate change data