William Ewart (26 December 1848, London – 11 August 1929, London) was an English physician remembered for Ewart's sign.
William Ewart was born in London to a French mother, and was educated partly in England and partly at the University of Paris. He studied medicine at St George's Hospital Medical School, qualifying LRCS in 1871 and LRCP in 1872. He gained his M.B. in 1877 from Cambridge University. He worked at St George's Hospital and the Royal Brompton Hospital, becoming a Fellow of the Royal College of Physicians in 1881 and Doctor of Medicine in 1882. He retired in 1907.