Baillie was a Scottish playwright, critic and poet who lived most of her life in Hampstead, where she was the centre of a rich literary culture. Born into a family of physicians and the daughter of a university professor, Baillie was unusually well educated for a woman of her time. As a teenager, she learned geometry, philosophy and Latin, and she had a lifelong interest in medicine.

Baillie wrote twenty-seven plays and was well known and widely admired during her lifetime. Her poetry was translated into other languages, and both Haydn and Beethoven set her songs to music. Written in an elegant, orderly style, her poetry dealt with heroic historical figures, Scottish songs, nature and childhood.

In addition to her literary work, Baillie was a supporter of other writers and a notable philanthropist who regularly gave away half of her earnings to charity. Passionately anti-slavery, she sponsored the first slave narrative published in England.