John Brennan may refer to:
Public officials Jack Brennan (1937–2023), U.S. Marine officer and aide of Richard Nixon John O. Brennan (born 1955), former CIA director John P. Brennan (1864–1943), Democratic politician in the U.S. state of Ohio John Brennan Hussey (born 1934), former mayor of Shreveport, Louisiana John Joseph Brennan (1913–1976), Northern Ireland politician John Brennan (Irish senator) (1901–1977), Fianna Fáil politician John A. Brennan Jr. (born 1945), American lobbyist and Massachusetts politician
Sports J. J. Brennan (1887–1943), Irish hurler John Brennan (Derry Gaelic footballer) (born 1942), Gaelic football manager and player John Brennan (Kerry Gaelic footballer), former Gaelic footballer Jack Brennan (footballer, born 1892) (1892–1942), English footballer for Bradford City and Manchester City John Brennan (American football) (1913–1982), American football player Jack Brennan (baseball) (1862–1914), American baseball catcher John Brennan (athlete) (1879–1964), American track and field athlete
Artists Johnny Brennan (born 1961), American actor, screenwriter and voice actor John Wolf Brennan (born 1954), Irish pianist, organist and composer
Other people John J. Brennan (businessman) (born 1954), chairman and CEO of The Vanguard Group John Calder Brennan (1908–1996), U.S. historian John Brennan (doctor) (c. 1768–1830), Irish doctor Sidney Czira (1889–1974), Irish journalist and revolutionary known by her pen name "John Brennan" John N. H. Brennan (1914–2010), Irish author, huntsman and solicitor John P. Brennan (priest) (c. 1836–1889), first American Catholic priest to declare bankruptcy John W. Brennan (born c. 1968), United States Army general
See also John Brenan (disambiguation) John O'Brennan, Irish political scientist