Sir William James Bull, 1st Baronet, PC (29 September 1863 – 23 January 1931) was an English solicitor and Conservative politician.
Bull was the son of Henry Bull, a solicitor, and his wife Cecilia Ann Howard, daughter of James Peter Howard. He was returned to Parliament for Hammersmith in 1900, a seat he held until 1918, and then sat for Hammersmith South until 1929.
Having been knighted in 1905, he was admitted to the Privy Council in 1918 and created a baronet, of Hammersmith in the County of London, in 1922.
Bull married Lilian Hester Brandon, daughter of Gabriel Samuel Brandon, on 5 January 1904. They had four sons. He died in January 1931, aged 67, and was succeeded in the baronetcy by his eldest son Stephen. His third son, Anthony Bull, was Chairman of London Transport from 1965 to 1971. His youngest son, Peter Bull, became a well-known character actor. Lady Bull died on 3 September 1963.
He compiled A History of the Broadway Congregational Church, Hammersmith, which was published in 1923.