Weir would not start writing full-time until the late 1990s. After organising it into chronological order, The Bodley Head agreed to publish it. She revised the work eight times over a twenty-two-year period, and decided that it might be 'of interest to others'.

Weir became a published author in 1989 with the publication of Britain's Royal Families, a compilation of genealogical information about the British Royal Family. In 1981, she wrote a book on Jane Seymour, which was again rejected by publishers, this time because it was too short. A revised version of this biography would later be published as her second book, The Six Wives of Henry VIII. Her work was deemed too long by publishers, and was consequently rejected. In the 1970s, Weir spent four years researching and writing a biography of the six wives of Henry VIII. Between 19, she ran a school for children with learning disabilities. Weir worked as a civil servant, and later as a housewife and mother to her children. She married Rankin Weir in 1972, with whom she had two children in the early 1980s. She opted to abandon history as a career after becoming disillusioned with 'trendy teaching methods'.

She was educated at City of London School for Girls and North Western Polytechnic and hoped to become a history teacher. Weir became interested in the field of history at the age of 14 after reading a book about Catherine of Aragon. She has described her mother as 'a genuinely good person with heaps of integrity, strength of character, humour and wisdom, and has overcome life’s trials with commendable fortitude.' Weir was born and raised in central London.

The ring and the crown alison weir