Georgia Ziadie was born in Jamaica in 1949, one of four children of Michael and Gloria Ziadie. She had a genital malformation (a fused labia and deformed clitoris). Medical advice at the time was to assign her as a male as they were the superior sex therefore would have been able to live a normal life she was christened George William. Though her family life was otherwise happy, Campbell has spoken and written of the struggles she faced being raised as a boy when she was physically female.
Her family, the Ziadies, were prominent in Jamaica. Their father was descended from one of six brothers who emigrated from Lebanon in the early 20th century; they were Maronite Catholics. Her mother was also Catholic, of English, Irish, Portuguese and Spanish descent, and her maternal great-grandmother was a Sephardic Jew.
Campbell moved from Jamaica to New York City to attend the Fashion Institute of Technology. She was not able to have corrective surgery until she was 21, when her grandmother discovered what had occurred and gave her the $5,000 she needed. At that time, Ziadie legally changed her name to Georgia Arianna and received a new birth certificate.
"No one ever faced the knife more eagerly than I. You would have thought I was going on a wonderful cruise – which, in a way, I suppose I was," Campbell wrote in her autobiography. She had already started working as a model in New York City prior to her surgery and was considered a great beauty.
On 23 March 1974, after having known him for only five days, she married Lord Colin Ivar Campbell, the younger son of the eleventh Duke of Argyll. She has said of him, "He had the strongest personality of anyone I had ever met – he simply exuded strength, decisiveness and charm." However their relationship quickly soured, and she left him after nine months, citing his abusiveness and drug addiction. The couple divorced after 14 months. She successfully sued several publications that claimed she was born a boy and had subsequently undergone a sex change, and accused her former husband of selling the untrue story for money.
In 1993, she adopted two Russian boys, Misha and Dima. She lives in Kennington, London.
In 2013 she purchased Castle Goring, a Grade I listed country house in Worthing, Sussex.
Campbell is best known for her books on Diana, Princess of Wales and Queen Elizabeth. Her 1992 book, Diana in Private: The Princess Nobody Knows, provided information about Diana's struggle with bulimia and her affair with James Hewitt. Campbell was dismissed as a fantasist, but some of her claims were later vindicated. Diana in Private appeared on the New York Times Best Seller list in 1992.
Campbell's 2009 book, Daughter of Narcissus: A Family's Struggle to Survive Their Mother's Narcissistic Personality Disorder, was well received.
Some of her books have been criticised for unverified statements. In The Queen Mother, The Untold story of Elizabeth Bowes Lyon (2012), Campbell claimed that Elizabeth and her brother were born to the family's French cook, who was used as a surrogate mother.
In November 2015, Campbell took part in the fifteenth TV series of I'm a Celebrity...Get Me Out of Here!. The following month, she left the programme "on medical grounds". In a later interview, Campbell said that she felt bullied into leaving the show by Tony Hadley and Duncan Bannatyne.
In 2016, she featured in a documentary entitled Lady C and the Castle, which was broadcast by ITV. The programme charted her journey in converting her dilapidated castle into a wedding venue. In 2017 she appeared at the castle in an episode of Salvage Hunters on Quest.The Queen Mother: The Untold Story of Elizabeth Bowes Lyon, Who Became Queen Elizabeth The Queen Mother. 2012.
Daughter of Narcissus: A Family's Struggle to Survive Their Mother's Narcissistic Personality Disorder. 2009. (Autobiography, profile of her mother)
The Real Diana. 2005. (A republication of her 1992 book, with sources)
Empress Bianca. 2005. (Withdrawn after legal threats from Lily Safra and subsequently reissued in 2008 with amendments)
A Life Worth Living. 1997. (autobiography)
The Royal Marriages: What Really Goes on in the Private World of the Queen and Her Family. 1993.
Diana in Private: The Princess Nobody Knows. 1992.
Lady Colin Campbell’s Guide to Being a Modern Lady. 1986.