McCullough was born in Wellington, in outback central west New South Wales, in 1937 to James and Laurie McCullough.. Her mother was a New Zealander of part-M?ori descent. During her childhood, her family moved around a great deal, and she was also "a voracious reader". Her family eventually settled in Sydney, and she attended Holy Cross College, having a strong interest in the humanities.

Before entering tertiary education, she previously earned a living as a teacher, librarian, and journalist. In her first year of medical studies at the University of Sydney she suffered dermatitis from surgical soap and was told to abandon her dreams of becoming a medical doctor. Instead, she switched to neuroscience and worked in Royal North Shore Hospital in Sydney.

In 1963 she moved for four years to the United Kingdom; at the Great Ormond Street hospital in London, she met the chairman of the neurology department at Yale University who offered her a research associate job at Yale. McCullough spent ten years from April 1967 to 1976 researching and teaching in the Department of Neurology at the Yale Medical School in New Haven, Connecticut, United States. It was while at Yale that her first two books were written.

The success of these books enabled her to give up her medical-scientific career and to try and "live on her own terms"In the late 1970s, after stints in London and Connecticut, USA, she finally settled on the isolation of Norfolk Island in the Pacific, where she met her husband, Ric Robinson (then aged 33), whom she married on 13 April 1983 (she was aged 46).

In 1984 a portrait of Colleen McCullough, painted by Wesley Walters, was a finalist in the Archibald Prize. The prize is awarded for the "best portrait painting preferentially of some man or woman distinguished in Art, Letters, Science or Politics".

The depth of historical research for the novels on ancient Rome led to her being awarded a Doctor of Letters degree by Macquarie University in 1993.

More recently, McCullough engendered criticism for controversial statements made during the Pitcairn sexual assault trial of 2004. McCullough asserted that the rapes committed by the defendants (all but one of whom were ultimately found guilty of at least some of the charges they faced) were "indigenous customs" and that "[i]t's Polynesian to break your girls in at 12."

In 2005, McCullough briefly appeared alongside family members in the 6 minute long short comedy Popcorn People.

McCullough is a member of the New York Academy of Sciences and is a fellow of the American Association for the Advancement of Science. She now lives in Sydney.

Her 2008 novel The Independence of Miss Mary Bennett engendered controversy with her reworking of characters in Jane Austen's Pride and Prejudice. Susannah Fullerton, the president of the Jane Austen Society of Australia, said she "shuddered" that Elizabeth Bennet was rewritten as weak, and Mr Darcy savage. "She is one of the strongest, liveliest heroines in literature [and] Darcy's generosity of spirit and nobility of character make her fall in love with him — why should those essential traits in both of them change in 20 years?"

McCullough's 1987 novel 'The Ladies of Missalonghi' relies heavily on a little known 1926 novel by Canadian author L.M. Montgomery, 'The Blue Castle'. In both novels, emotionally deprived single women shake off the shackles of restrictive and restricted home lives to marry outside of their known social circles. In each, a key plot device is the women's persuading the men to marry them against their initial inclination by convincing them that they, the women, have only a short time to live. The source of the idea in each case is a degree of confusion (complete confusion in Montgomery's book)of a patient's name and diagnosis. In both cases, love develops, the men turn out to be wealthy, and the endings are happy, if overly contrived. The general tone and domestic details of the two books are quite similar as well, though McCullough's is more open about sexuality. This entry is based on the Linda Van Buskirk's readings of the novels and has not been published. Dr. Van Buskirk is a senior lecturer in the Department of Communication, Cornell University.

Novels

• Tim (1974)
• The Thorn Birds (1977)
• An Indecent Obsession (1981)
• A Creed for the Third Millennium (1985)
• The Ladies of Missalonghi (1987)
• The Song of Troy (1998)
• Morgan's Run (2000)
• The Touch (2003)
• Angel Puss (2004)
• On, Off (2006)
• The Independence of Miss Mary Bennet (2008)

Biography

• The Life of Roden Cutler VC (1999)

Masters of Rome Series

1. The First Man in Rome (1990)
2. The Grass Crown (1991)
3. Fortune's Favorites (1993)
4. Caesar's Women (1996)
5. Caesar (1997)
6. The October Horse (2002)
7. Antony and Cleopatra (2007)

Carmine Delmonico series

1. On, Off (2006)
2. Too Many Murders (December 2009)