Lewis was born in Chicago, Illinois, and a graduate of the University of Chicago, where she was a member of a literary circle including Glenway Wescott, Elizabeth Madox Roberts, and her future husband Yvor Winters. She was an active member of the University of Chicago Poetry Club. She taught at both Stanford University in California, and at the University of California at Berkeley.

She wrote The Wife of Martin Guerre (1941) which is the tale of one man's deception and another’s cowardice. Her first novel was The Invasion: A Narrative of Events Concerning the Johnson Family of St. Mary's (1932). Other prose works include The Trial of Soren Qvist (1947), The Ghost of Monsieur Scarron (1959), and the volume of short fiction, Good-bye, Son, and Other Stories (1946).

Lewis was also a poet, and concentrated on imagery, rhythms, and lyricism to achieve her goal. Among her works are The Indians in the Woods (1922), and the later collections Poems, 1924-1944 (1950), and Poems Old and New, 1918-1978 (1981). She also collaborated with Alva Henderson, a composer for whom she wrote three libretti and several song texts.

She married the American poet and critic Yvor Winters in 1926. Together they founded Gyroscope, a literary magazine that lasted from 1929 until 1931.

Lewis died at her home in Los Altos, California, in 1998, at the age of 99.

Poetry

• The Indians in the Woods. Published by Monroe Wheeler, as Manikin Number One, Bonn, Germany, n.d. [1922].
• The Wheel in Midsummer Lynn, Mass, The Lone Gull, 1927.
• The Earth-Bound' Aurora, New York, Wells College Press, 1946
• Poems 1924 – 1944 Denver, Alan Swallow, 1950
• The Ancient Ones Portola Valley, California: No Dead Lines, 1979
• The Indians in the Woods 2nd edition with new preface, Palo-Alto California, Matrix Press, 1980.
• Poems Old and New 1918 – 1978 Chicago/Athens, Ohio: Swallow Press / Ohio University Press 1981
• Late Offerings Florence, Ky, Robert L. Barth, 1988
• Janet and Deloss: Poems and Pictures San Diego, Brighton Press 1990
• The Dear Past and other poems 1919 – 1994 Edgewood Ky, Robert L. Barth, 1994
• The Selected Poems of Janet Lewis thens Ohio, Swallow Press / Ohio University Press, 2000, ISBN 978-0804010238.