John, Johnny, or Jack Leonard may refer to:
Arts and entertainment John Leonard (songwriter) (fl. 1800s–1810s), English poet and songwriter Jack E. Leonard (1910–1973), American comedian and actor John Leonard (critic) (1939–2008), American literary and film critic John Leonard (poet) (born 1965), Australian poet
Law and politics John E. Leonard (1845–1878), American politician from Louisiana John Leonard, Baron Leonard (1909–1983), British politician John Leonard (judge) (1926–2002), British judge
Sports Jack Leonard (hurler) (1873–1938), Irish hurler Jack Leonard (footballer) (1876–?), English footballer Johnny Leonard (1903–1995), Australian rules footballer John Leonard (canoeist) (born 1948), New Zealand sprint canoeist John Leonard (Gaelic footballer) (born 1976), Irish Gaelic footballer John Leonard (ice hockey) (born 1998), American ice hockey player
Others John Leonard (bishop) (1829–1908), Irish bishop John Leonard (architect) (1857–1932), English architect John B. Leonard (1864–1945), American civil engineer John W. Leonard (1890–1974), US Army general J. Paul Leonard (1901–1995), American academic John J. Leonard, American roboticist
See also John Leonardi (1541–1609), Roman Catholic saint John Lennard (disambiguation)