O'Kelly is a surname. Notable people with the surname include:
- Aloysius O'Kelly (1853–1936), Irish painter, brother of James Joseph O'Kelly
- Auguste O'Kelly (1829–1900), music publisher in Paris
- Christopher O'Kelly (1895–1922), Canadian recipient of the Victoria Cross
- Don O'Kelly (1924–1966), American actor
- Edward Peter O'Kelly (1846–1914), Irish politician
- Gabriel O'Kelly (died 1731), Irish clergyman
- George O'Kelly (1831–1914), Franco-Irish pianist and composer
- Henri O'Kelly (1859–1938), Franco-Irish composer, pianist and organist
- James O'Kelly (1735–1826), American Methodist clergyman
- James Joseph O'Kelly (1845–1916), Irish politician
- John J. O'Kelly (1872–1957), Irish politician
- Joseph O'Kelly (1828–1885), Franco-Irish composer and pianist
- Malcolm O'Kelly (born 1974), Irish rugby player
- Roger Demosthenes O'Kelly (1880–1962), African-American lawyer
- Seán T. O'Kelly (1882–1966), Irish politician, second President of Ireland
- Seumas O'Kelly (1881–1918), Irish writer