She lives in Surrey, England. Before becoming an author, Weir worked as a teacher of children with special needs. She received her formal training in history at teacher training college.

Weir married Rankin Weir in 1972, and has two children, John (born 1982) and Kate (born 1984).

Weir retains a wide following of loyal readers. All of her books are best-sellers in the UK. In 2007, she completed her first novel Innocent Traitor, based on the life of Lady Jane Grey (1537—1554). Her second novel is The Lady Elizabeth which deals with the life of Queen Elizabeth I before her ascension to the throne. It was published in 2008 in the UK and United States. Her newest novel, The Captive Queen, was released in the summer of 2010 and is about Eleanor of Aquitaine.

On 4 February 2009, at a book-reading in Houston, Texas, Weir announced she will have a new book released in the UK covering the last four months of Anne Boleyn's life. This release is scheduled for October 2009. She also revealed that she currently has two more biographies and two novels in the works.

Traitors of the Tower is a novella written by Weir and published on World Book Day 2010. Working with Quick Reads and BBC raw, Weir has recorded the first chapter as a taster and introduction to get people back into the habit of reading.

Nonfiction

• The Six Wives of Henry VIII (1991)
• The Princes in the Tower (1992)
• Lancaster and York - The Wars of the Roses (1995)
• Children of England: The Heirs of King Henry VIII (1996, later reissued as The Children of Henry VIII)
• Elizabeth, The Queen (1998)
• Eleanor of Aquitaine: By the Wrath of God, Queen of England (1999)
• Henry VIII: The King and His Court (2001)
• Britain's Royal Families: The Complete Genealogy (latest edition, 2002)
• Mary, Queen of Scots and the Murder of Lord Darnley (2003)
• Isabella: She-Wolf of France, Queen of England (2005)
• Katherine Swynford: The Story of John of Gaunt and His Scandalous Duchess (2007)
• The Lady in the Tower (2009)
• Traitors of the Tower (2010)

Fiction

• Innocent Traitor: A Novel of Lady Jane Grey (2007)
• The Lady Elizabeth (2008)
• The Captive Queen (2010)