Haywood gave conflicting accounts of her own life; her origins remain unclear and there are presently contending versions of her biography. For example, it was once mistakenly believed that she married the Rev. Valentine Haywood.
Some details have been widely accepted however: She was probably born in either Shropshire or London, England. Her first entry into the public record is in Dublin, Ireland, in 1715 when she was listed as "Mrs. Haywood" in Thomas Shadwell's Shakespeare adaptation, Timon of Athens; or, The Man-Hater at the Smock Alley Theatre. She had an open live-in relationship with William Hatchett, the father of her second child. She also had a child with Richard Savage.
William Hatchett was a bookseller who shared a stage career with Haywood, and the couple were lovers and companions for more than twenty years. They collaborated on an adaptation of The Tragedy of Tragedies by Henry Fielding and an opera, The Opera of Operas; or, Tom Thumb the Great (1733).
Haywood’s writing career began in 1719 with the first instalment of Love in Excess, a novel, and ended in the year she died with conduct books The Wife and The Husband, and the biweekly periodical The Young Lady. She wrote in several genres and many of her works were published anonymously. There is much of Haywood’s writing career that still remains unknown.
She fell ill in October 1755 and died on 25 February 1756. She was buried in Westminster. For unknown reasons, her burial was delayed by about a week and her death duties remain unpaid.