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
 * Billy Brennan (born 1934), British ice hockey player