William O'Neil (1933–2023) was an American businessman and stockbroker.
William O'Neil may also refer to:
William O'Neil (Wisconsin politician) (1848–1917), American politician William A. O'Neil (1927–2019), Canadian civil servant, Secretary-General of the International Maritime Organization William T. O'Neil (1850–1909), American politician from New York
See also William O'Neal (disambiguation) William O'Neill (disambiguation)