John Hennessey or Hennessy may refer to:
Religious figures John Hennessy (bishop) (1825–1900), American Roman Catholic archbishop of Dubuque, Iowa John Joseph Hennessy (1847–1920), Irish-born prelate of the Roman Catholic Church in Kansas
Sportspeople John F. Hennessey (1900–1981), American tennis player John Hennessey (rugby league), Welsh rugby league footballer John Hennessy (American football) (born 1955), American football player Jackie Hennessy (born 1940), Irish footballer
Politics Jack Hennessy (politician) (John F. Hennessy, 1951–2024), American Democratic Party politician member of the Connecticut House of Representatives John Pope Hennessy (1834–1891), Irish Westminster MP, Governor of Hong Kong, grandfather of John Pope-Hennessy
Others John A. Hennessy (1859–1951), American special investigator John David Hennessey (1847–1935), English-Australian author, newspaper editor and Protestant minister John J. Hennessey (1921–2001), American four-star army general John L. Hennessy (born 1952), American computer scientist; former president of Stanford University John M. Hennessy (born 1936), American financier and philanthropist John Pope-Hennessy (1913–1994), British art historian and museum director, grandson of John Pope Hennessy John W. Hennessey Jr. (1925–2018), American academic and educator
See also Jack Hennessy (disambiguation) Hennessey (disambiguation)