Hannah Cowley (née Parkhouse; 14 March 1743 – 11 March 1809) was an English playwright and poet. Although Cowley's plays and poetry did not enjoy wide popularity after the 19th century, critic Melinda Finberg rates her as "one of the foremost playwrights of the late eighteenth century" whose "skill in writing fluid, sparkling dialogue and creating sprightly, memorable comic characters compares favourably with her better-known contemporaries, Goldsmith and Sheridan." Cowley's plays were produced frequently in her lifetime. The major themes of her plays – including her first, The Runaway (1776), and her major success, which is being revived, The Belle's Stratagem (1780) – revolve around marriage and how women strive to overcome the injustices imposed by family life and social custom.

Born Hannah Parkhouse, she was the daughter of Hannah (née Richards) and Philip Parkhouse, a bookseller in Tiverton, Devon. Sources disagree about some details of her married life, citing her marriage date as either 1768 or 1772 and claiming she had either three or four children. Shortly after her marriage to Thomas Cowley, the couple moved to London, where Thomas worked as an official in the Stamp Office and as a part-time journalist.

The introduction to her 1813 collected works gives an account of how Cowley was struck by a sudden desire to write while attending a play with her husband. "So delighted with this?" she boasted to him. "Why I could write as well myself!" Thomas teased her, but by the middle of the next day Cowley showed him the first act of her comedy The Runaway. If the substance of the story is true, this visit to the theatre could have occurred no later than 1775, for the rest of The Runaway was written, sent to the actor-manager David Garrick and produced at Drury Lane theatre by 15 February 1776.

The Runaway enjoyed 17 performances in its first season at Drury Lane and 39 in London by 1800, a success that encouraged Cowley to write more, though her mentor Garrick retired after the 1776 season. She wrote her next two plays, the farce Who's the Dupe? and the tragedy Albina, before the year was out.

Who's the Dupe? and Albina encountered difficulties in production. The new manager of Drury Lane, Richard Brinsley Sheridan, shelved The Runaway for most of the 1777 season. Miffed, Cowley sent Albina to Drury Lane's rival theatre in London, Covent Garden, but it met with no better reception there and the script alternated between the theatres for the next two years. Meanwhile, Sheridan agreed to produce Who's the Dupe?, but delayed its 1779 première until late spring, an unprofitable time for a new play to open.

The production of Albina generated public controversy for Cowley. While this play was bouncing between Drury Lane and Covent Garden, writer Hannah More's plays Percy (1777) and The Fatal Falsehood (1779) opened at Covent Garden. Watching Percy aroused Cowley's suspicions: Fatal Falsehood confirmed Cowley's belief that More had plagiarised from Albina.

As Cowley later wrote in her preface to the printed edition of Albina, hers and More's plays do indeed have "wonderful resemblances". Fatal Falsehood's opening on 6 May 1779, was followed by press charges (perhaps written by Thomas Cowley) that More stole her ideas from Cowley. On 10 August, More wrote to the St. James Chronicle to protest that she "never saw, heard, or read, a single line of Mrs. Cowley's Tragedy." In her preface to Albina, Cowley allows that the theatre managers, who in those days doubled as script editors, may have inadvertently given More her ideas: "Amidst the croud of Plots, and Stage Contrivances, in which a Manager is involv'd, recollection is too frequently mistaken for the suggestions of imagination" [emphasis in original].

Although she continued to enjoy a brilliant literary career, More wrote no more for the stage after her paper war with Cowley. Albina finally opened on 31 July 1779 at the Haymarket, a summer theatre more practised in staging comedies. It was neither a financial nor a critical success.