Mary worked at various things before she established herself as an author.
Her first "position" was as a traveling companion to a Widow Dawson of Bath. She maintained this position from 1778 until she was called home to nurse her mother in 1781.
In 1784, Mary opened a school at Newington Green in Islington with her two sisters and her friend, Fanny Blood. Fanny left to marry and moved to Lisbon. During Fanny's pregnancy she sent for Mary. Upon Mary's return to the school in 1786, she found the school had declined in her absence and she was forced to shut it down.
Still keeping with an educational trend, Mary became a governess to the daughters of Lord Viscount Kingsborough in 1786. She wrote her first book while working as a governess, but she was dismissed in 1787.
In 1788, Mary began to work for her publisher, Joseph Johnson, first as a translator and then as a reviewer for his monthly periodical, The Analytical Review.
Although she wrote quite a bit, her first real success as an
author came in 1790, when A Vindication of the Rights of Men
was published. She was then firmly established as an author.