William Brennan

William Brennan may refer to:

• William Brennan (Australian politician) (1865–1937), member of the New South Wales Parliament
• William Brennan (baseball) (born 1963), American baseball pitcher
• William C. Brennan (1918–2000), New York politician and judge
• William J. Brennan Jr. (1906–1997), justice of the United States Supreme Court
• William John Brennan (1938–2013), Australian Roman Catholic bishop
• William Joseph Brennan (bishop) (1904–1975), Roman Catholic priest in Australia
• Will Brennan (born 1998), American baseball player
• Willis Brennan (1893–1950), American football player
• Willy Brennan (died 1804), Irish highwayman
• Bill Brennan (umpire) (1880–1933), Major League Baseball umpire and college football coach
• Bill Brennan (boxer) (1893–1924), American boxer
• Bill Brennan (activist) (born 1968), candidate for Governor of New Jersey in 2017
• Bill Brennan (journalist), American sports journalist
• Bill Brennan (Nebraska politician) (1922–1979), member of the Nebraska Legislature
• Billy Brennan (1934–2020), British ice hockey player