Kidman's ancestry includes Irish, Scottish and English heritage.
Kidman was born 20 June 1967, in Honolulu, Hawaii, while her Australian parents were temporarily in the United States on student visas. Her father was Antony Kidman (1938–2014), a biochemist, clinical psychologist and author, who died of a heart attack in Singapore aged 75. Her mother, Janelle Ann (née Glenny), is a nursing instructor who edited her husband's books and was a member of the Women's Electoral Lobby.
Being born in Hawaii, she was given the Hawaiian name "Hōkūlani". The inspiration for the name came from a baby elephant born around the same time at the Honolulu Zoo, but the name is also a commonly used Hawaiian name for girls, Hokulani meaning 'Heavenly Star'.
At the time of Kidman's birth, her father was a graduate student at the University of Hawaiʻi at Mānoa. He became a visiting fellow at the National Institute of Mental Health of the United States. Opposed to the war in Vietnam, Kidman's parents participated in anti-war protests while living in Washington, D.C. The family returned to Australia when Kidman was four and her mother now lives on Sydney's North Shore. Kidman has a younger sister, Antonia Kidman, a journalist and TV presenter.