William O'Brien may refer to:
Politicians William O'Brien (Irish nationalist politician) (1852–1928), Irish journalist and politician William O'Brien, 2nd Earl of Inchiquin (c. 1640–1692), Governor of Jamaica William O'Brien (Australian politician) (1882–1953), New South Wales politician William O'Brien (Fine Gael politician) (1918–1994), Irish Fine Gael TD and Senator from County Limerick William O'Brien (Minnesota politician) (1930–2007), American politician William O'Brien (Nova Scotia politician) (1782–1854), political figure in Nova Scotia William O'Brien (Rhode Island politician) (born 1969), American state legislator in Rhode Island William O'Brien (trade unionist) (1881–1968), Irish Labour TD and trade union leader William Edward O'Brien (1831–1914), lawyer, farmer, editor and political figure in Ontario, Canada William H. O'Brien (1871–?), Wisconsin state assemblyman William J. O'Brien (politician) (1836–1905), United States Representative from Maryland, 1873–1877 William L. O'Brien (born 1951), former Speaker of the New Hampshire House of Representatives William Smith O'Brien (1803–1864), Irish Conservative and Repeal MP and Young Ireland revolutionary William Smith O'Brien (American politician) (1862–1948), U.S. Representative from West Virginia Bill O'Brien (British politician) (1929–2025), British Labour MP for Normanton, 1983–2005 Billy O'Brien (politician) (1929–2012), American politician in the Virginia House of Delegates
In sports William O'Brien (American football) (1923–2000), head football coach for the Southern Illinois Salukis William O'Brien (footballer), Scottish footballer William O'Brien (racing driver) (born 1959), American racing driver Parry O'Brien (William Patrick O'Brien, 1932–2007), American shot-put innovator William O'Brien, National League baseball umpire in 1876 Willie O'Brien (1929–2015), English footballer Bill O'Brien (American football, born 1924) (1924–2005), American football halfback Bill O'Brien (American football) (born 1969), American football coach Bill O'Brien (footballer, born 1877) (1877–1942), Australian rules footballer for Collingwood Bill O'Brien (footballer, born 1887) (1887–1943), Australian rules footballer for St Kilda Bill O'Brien (footballer, born 1905) (1905–1988), Australian rules footballer for South Melbourne Billy O'Brien (baseball) (1860–1911), Major League Baseball first baseman Billy O'Brien (footballer) (born 1995), Welsh football goalkeeper
Other people William O'Brien, 2nd Marquess of Thomond (1765–1846), Irish peer William O'Brien, 3rd Earl of Inchiquin (1662–1719), Irish peer William O'Brien, 4th Earl of Inchiquin (1700–1777), founder of the Royal Cork Yacht Club in 1720 William O'Brien (actor) (1740–1815), Irish actor in the company of David Garrick at Drury Lane William O'Brien (judge) (1832–1899), Irish judge William O'Brien (police officer) (1944–2016), American police officer William O'Brien (Royal Navy officer) (1916–2016), British admiral William O'Brien, President, BATS Global Markets William B. O'Brien, founder and the president of the World Federation of Therapeutic Communities also co-founder of Daytop William David O'Brien (1878–1962), auxiliary bishop of Chicago, Illinois, USA William J. O'Brien (Medal of Honor) (1899–1944), United States Army officer during World War II William J. O'Brien, inventor of the Decca Navigator System William P. O'Brien (police commissioner) (1891–1960), American police officer William S. O'Brien (1825–1878), American businessman Bill O'Brien (actor), Director of Theatre and Musical Theatre for the National Endowment for the Arts; actor Tim O'Brien (author) (William Timothy O'Brien, born 1946), American author Billy Porter (criminal) (William O'Brien, 1850–?), American burglar and underworld figure in New York City William O'Brien (archaeologist), Irish professor of archaeology in University College Cork. Billy O'Brien, film director whose work includes I Am Not a Serial Killer (film) (2016) Billy O'Brien, child actor who appeared in films including The Lone Trail (1932)
Other uses SS William O'Brien, steam cargo ship built in 1914–1915 by New York Shipbuilding Company of Camden, foundered in April 1920
See also Will O'Brien (disambiguation) William O'Bryan (1778–1868), English preacher