U.S. writer and advocate of women's rights and health reform.

Nichols is best known as a promoter of hydropathy—the use of water-cures, cold baths, and vegetarianism to cure illness. She edited the Health Journal and Advocate of Physiological Reform in 1840, and lectured widely on woman's hygiene, physiology, and anatomy. In 1845 she founded a water-cure establishment in New York City and also began writing magazine articles and, under the pen name Mary Orme, fiction. Married in 1831 to Hiram Gove and later divorced, she married Thomas Low Nichols in 1848.

By 1850 Mary Nichols was a leading contributor to the Water-Cure Journal and in 1851 was a founder of the American Hydropathic Institute. She later published, with her husband, Nichols' Journal of Health, Water-Cure, and Human Progress, which espoused hydropathy, vegetarianism, free love, and spiritualism. Her writings include Lectures to Ladies on Anatomy and Physiology (1842) and the autobiographical Mary Lyndon (1855).