John Gannon may refer to:
- John Gannon (Australian politician) (1830–1887), member of the New South Wales Legislative Assembly
- John Gannon (footballer) (born 1966), English footballer
- John D. Gannon (1948–1999), American computer scientist
- Sam Gannon (born 1947), real name John Gannon, Australian cricketer
- John Mark Gannon (1877–1968), American clergyman of the Roman Catholic Church
- John Gannon (American politician), Idaho State Representative
John Thomas Gannon was an Australian politician.
John Gannon is an English former professional footballer, featuring mainly for Sheffield United.
John D. Gannon was a prominent Computer Scientist, Professor and Chair of the Department of Computer Science University of Maryland, at College Park. Gannon was a leading researcher in software engineering, specifically the specification, analysis, and testing of software systems.
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