Eleanor Dark was born Eleanor O'Reilly at Burwood in Sydney in 1901, the only daughter of writer Dowell O'Reilly (q.v.). She was educated at a number of Sydney schools, including Redlands, but did not attend university because she failed to meet the mathematics requirement for admission. Instead, she learned typing and shorthand, starting work at a solicitor's office in 1920. In 1922 she married Dr Eric Payten Dark, a general practitioner. They moved to Katoomba in 1923 and, except for a few periods, remained there for the rest of their lives. In 1929 their only child, Brian Michael, was born.
Devoted to maintaining a comfortable home for her family, Eleanor Dark pursued her writing when time permitted. She began contributing verse and short stories to magazines in 1921 and had completed nine novels by the 1950s. The most well-known of these is The Timeless Land (1941), the first instalment of a trilogy that dramatizes the first years of European settlement in Australia. In 1941 The Timeless Land was selected as the Book of the Month by the Book of the Month Club in the U.S.A. and was adapted for television in 1980 by the Australian Broadcasting Corporation. Dark was influenced by the major European writers of the 1920s and 1930s, adopting a psychological focus and a concern for the perception of time. Dark's psychological focus was used to great success in The Little Company (1945) where the personal and political attitudes of war-time Australians are explored. Dark's novels also explore social issues such as women's rights and the plight of Aborigines.
Dark was a founding member of the Australian Book Society in 1945.
Eleanor Dark has received a number of awards for her contributions to Australian literature and in 1977 she was made an Officer of the Order of Australia (AO). She died in 1985.