John Barnett (1802–1890) was an English composer.
John Barnett may also refer to:
- John Barnett (Australian rules footballer) (born 1975), former Australian rules footballer
- John Barnett (rugby) (1880–1918), Australian rugby union and rugby league player
- John Francis Barnett (1837–1916), English music composer and teacher
- John Davis Barnett (1848–1926), early Canadian curator-librarian
- Jack Barnett (baseball) (1879–1923), baseball player
- John Maughan Barnett (1867–1938), New Zealand organist, choirmaster and conductor
- John W. Barnett (1800–1876), Texas farmer, merchant and community leader
- John Manley Barnett (1917–2013), American conductor
- John Barnett (whistleblower) (1962–2024), Boeing whistleblower