Hennessy is an Irish surname, being the anglicised form of Ó hAonghusa. A variant is Hennessey.
Notable people with the surname include:
Arthur Hennessy (1876–1959), Australian pioneer rugby league identity Bill Hennessy (disambiguation), several people Carly Smithson (née Hennessy, born 1983), Irish singer Charles O'Connor Hennessy (1860–1936), American politician from New Jersey Christie Hennessy (1945-2007), Irish singer Claire Hennessy (born 1986), Irish novelist Clinton Hennessy (born 1977), Irish sportsperson David Hennessy (disambiguation), several people Esmé Frances Hennessy (1933–2023), South African botanist George Hennessy, 1st Baron Windlesham (1877, 1953), British soldier and Conservative politician Jean Hennessy (1874–1944), French politician and member of the Hennessy family Jacqueline Hennessy (born 1968), journalist Jill Hennessy (born 1968), film and television actress Joe Hennessy (born 1956), former Irish sportsperson John Hennessy (disambiguation), several people Josh Hennessy (born 1985), professional ice hockey player Kevin Hennessy (born 1961), Irish retired sportsperson Larry Hennessy (1929–2008), American basketball player Liv Hennessy, English playwright Matt Hennessy (born 1997), American football player Matthew Hennessy, Irish computer scientist Neil Hennessy (born 1978), musician and music producer/engineer Patrick Hennessy (disambiguation), several people Peter Hennessy (born 1947), English historian of government Ryan Hennessy (born 1995), Irish singer and musician Séamus Hennessy (hurler, born 1989), Irish sportsperson Swan Hennessy (1866–1929), Irish-American composer resident in Paris Thomas Hennessy (politician), Irish politician Thomas Hennessy (American football) (born 1994), American football player W. Louis Hennessy (born 1955), 4th Circuit Court Associate Judge in Maryland, former Maryland Delegate William Hennessy (disambiguation), several people