Eleanor Dark was born in Sydney. She was the second of three children born to the poet, writer and parliamentarian, Dowell Philip O'Reilly and his wife, Eleanor McCulloch O'Reilly. On finishing school and unable to enter university, having failed mathematics, she learnt typing and took a secretarial job. In 1922 she married Dr Eric Payten Dark, a general practitioner who wrote books, articles and pamphlets on politics and medicine. Dr Eric Payten Dark (1889—1987) was an active member of the Labor left in New South Wales, was involved in contemporary political debate and was a committed socialist, although never a member of the Communist Party. His books include The World Against Russia and Who are the Reds. They lived in Katoomba, New South Wales, where Eleanor wrote eight of her ten novels, including short stories and articles.

In the 50s the Darks bought a farm in Queensland where they spent part of the year for seven years. Eleanor wrote her last published work, Lantana Lane at the farm. Their son Michael had also moved to Queensland where he eventually married and had two daughters. The move to Queensland has, by some, been associated with the desire to escape a growing sense of persecution and isolation within the Katoomba community due to growing attacks on members of Left wing parties in the press and by the Menzies Government. Dr Dark's political writing and involvement in Left wing circles attracted attention from anti communist elements within the Menzies Government and the Australian Security Intelligence Organisation (ASIO). Like many writers and social commentators of the time, who were critical of Menzies or were Left wing, it is certain that the Darks were under surveillance. This surveillance extended to Eric Dark's first son from his first marriage, John Dark, and possibly to his second son with Eleanor, Michael Dark.

The Darks' second son, Michael, inherited the family home 'Varuna' in Katoomba, which in 1988 was turned into a writers' centre, managed by the Eleanor Dark Foundation, of which Michael Dark remains President. The centre has retained its name, and is known as Varuna — The Writers' House.

Eleanor Dark's best known work is The Timeless Land (1941), the first part of a trilogy, with Storm of Time (1948) and No Barrier (1953).

Novels

• Slow Dawning. (1932)
• Prelude to Christopher. (1934)
• Return to Coolami. (1936)
• Sun Across the Sky. (1937)
• Waterway. (1938)
• The Little Company. (1945)
• The Timeless Land. (1941)
• Storm of Time. (1948)
• No Barrier. (1953)
• Lantana Lane. (1959)