Marian Irwin Osterhout (June 16, 1888 – May 10, 1973), was an American plant physiologist born in Japan. She was the first woman to receive a National Research Council fellowship.
Marian Irwin was born in Tokyo, the daughter of Iki Takechi Irwin (1857–1940) and Robert Walker Irwin (1844–1925). Her mother was a Japanese noblewoman, daughter of a samurai; her father was an American diplomat, the son of William W. Irwin and a direct descendant of Benjamin Franklin. Her older sister Bella Irwin founded a school in Tokyo. Their aunt, Agnes Irwin, was also an educator, the first dean of Radcliffe College.
Marian Irwin was educated in Japan and at Bryn Mawr College, where she earned a bachelor's degree in 1913. She earned a doctoral degree in biology, at Radcliffe College in 1919, as a student of George Howard Parker. Her dissertation title was "Effect of Electrolytes and Non-electrolytes on Organisms in Relation to Sensory Stimulation and Respiration."