Mary Fairchild was born in New Haven, Connecticut. She studied art at the St. Louis School of Fine Art and at Acadamie Julian in Paris.
She married sculptor Frederick MacMonnies in 1888. She resided in Paris, spending summers in Giverny. The couple summered with their two daughters in a 14th-century monastery in Giverny. She later divorced and married painter Will Low in 1909. Her portraiture received acclaim at the 1893 Chicago Exposition. she exhibited regularly at the Paris Salon between 1886 and 1907. She won awards icluding membership in the National Academy of Design.
Fairchild 's work reflects several phases of development. In the beginning She worked in a sunlit style reminiscent of her professor at Acadamie Julian. Later, however, her work became more tonal and misty. She painted her portraits in very dark colors after her second marriage but gradually returned to a lighter, Impressionistic palette in the final phase of her career.