John O'Reilly may refer to:
- John O'Reilly (baseball) (born 1995), American baseball player
- John O'Reilly (soldier) (born 1908), Irish soldier
- John O'Reilly (politician) (born 1951), Canadian politician
- John O'Reilly (composer) (born 1940), composer and music theorist
- John O'Reilly (cricketer) (born 1930), Australian cricketer
- John B. O'Reilly Jr. (born 1948), mayor of Dearborn, Michigan
- John Boyle O'Reilly (1844–1890), poet and novelist
- John Francis O'Reilly (1888–1942), Australian politician
- John Joseph O'Reilly (1888–1933), Australian politician
- John O'Reilly (engineer) (born 1946), vice-chancellor of Cranfield University
- John Joe O'Reilly (politician) (1881–1967), Irish politician
- John Joe O'Reilly (Gaelic footballer) (1919–1952)