Many noteworthy people have had the name John O'Neill

• In 1866, one John O'Neill led 800 Fenian raiders across the Niagara River at Buffalo, New York/Fort Erie, Ontario, as part of an effort to free Ireland from the English as part of the Fenian Invasion of Canada .
• In 1971, a Vietnam War veteran named John Ellis O'Neill debated John Kerry (who later became a candidate in the 2004 presidential election) on The Dick Cavett Show. O'Neill later helped to form the anti-Kerry group Swift Boat Veterans for Truth.
• John P. O'Neill (1952–September 11, 2001) was an FBI agent who investigated terrorism and Al Qaeda in the late 1990s. He left the bureau and became head of security at the World Trade Center shortly before the September 11, 2001 attacks.
• Another John O'Neill is the head of the Australian Soccer Association.
• John O'Neill, 1926-1999: was a professional musician from County Durham, England famous for his whistling abilities. He had a hit in 1967 with the song I Was Kaiser Bill's Batman, was a regular on the Black and White Minstrel Show and was a session singer on many television programmes such as Monty Python's Flying Circus and the Morecambe and Wise Show. His most well known achievment however was the whistling on the theme tune to The Good, The Bad and The Ugly.