John Dennis may refer to:
- John Dennis (dramatist) (1657–1734), English dramatist
- John Dennis (1771–1806), Maryland congressman
- John Dennis (1807–1859), his son, Maryland congressman
- John Stoughton Dennis (1820–1885), Canadian surveyor
- John B. Dennis (1835-1894), American Union Civil War era brevet brigadier general
- John Dennis (carmaker) (1871–1939), English carmaker, partner with Raymond Dennis in Dennis (which became Dennis Specialist Vehicles)
- John William Dennis, Member of Parliament for Birmingham Deritend, 1918–1922
- John Dennis (Missouri politician) (1917–2000), Missouri politician
- John Dennis (bishop) (born 1931), former Bishop of St Edmundsbury and Ipswich
- John E. Dennis (born 1939), mathematician
- John Dennis (talk show host) (born c. 1952), American radio talk show host
- John Dennis (California politician) (born 1963), American businessman and politician