John Harrison (1693–1776) was a clockmaker who designed and built the world's first successful marine chronometers.
John Harrison may also refer to:
- John Harrison (MP for Dunwich) (died 1558)
- John Harrison (died 1669) (1590–1669), English politician, MP for Lancaster
- John Harrison (diplomat) (fl. 1610s), 17th century English diplomat
- John Scott Harrison (1804–1878), American Congressman for Ohio; son of President William Henry Harrison and father of President Benjamin Harrison
- John B. Harrison (1861–1947), American jurist; Oklahoma Supreme Court justice
- John Harrison (Canadian politician) (1908–1964), Canadian MP for Meadow Lake, Saskatchewan
- John C. Harrison (judge) (1913–2011), American jurist; Montana Supreme Court justice
- Richard Harrison (New Zealand politician) (John Richard Harrison, 1921–2003), New Zealand politician
- John C. Harrison (law professor) (fl. 1970s–2020s), American law professor
- John Harrison (mayor) (fl. 1980s–2020s), English politician; mayor of North Tyneside
- John Harrison (Brookside), fictional character on the defunct British TV soap opera Brookside
- Khan Noonien Singh, the antagonist from Star Trek Into Darkness (John Harrison given as false name)
- John Harrison, fictional character on the American TV series Popular