William O'Neil (disambiguation)

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