William O'Brien
William O'Brien is the name of the following people:
- William O'Brien, 4th Earl of Inchiquin (1700–1777), Irish politician
- William O'Brien (politician, 1852) (1852-1928), Irish politician
- William O'Brien (Admiral) (born 1916), British admiral
- William O'Brien (politician, 1918) (1918-1994), Irish politician
- William B. O'Brien († 2014), American priest and addiction therapist
- William David O'Brien (1878–1962), American clergyman, auxiliary bishop in Chicago
- William J. O'Brien (1836-1905), American politician
- William L. O'Brien (* 1951), American lawyer and politician
- William Smith O'Brien (politician, 1803) (1803–1864), Irish politician
- William Smith O'Brien (Politician, 1862) (1862–1948), American politician (West Virginia)
- William X. O'Brien (1881–1968) Irish politician
William O'Brien referred to
- SS William O'Brien , built 1914–1915 in New York, sunk in 1920