Marchant was the daughter of Langworthy and Maude Marchant, and moved with her family to Washington, D.C. at age six.

After earning her undergraduate degree, followed in 1933 by her law degree from the National University of Washington, D.C. (now George Washington University), she was admitted to practice in Virginia and Washington D.C., and before the U.S. Court of Claims and the U. S. Supreme Court.

One of the first women to pass the bar in Washington DC, she served the World Bank as an attorney in the Legal Department for 18 years until retiring in 1972.

As Sarah Aldridge, she was the author of many literary works. Her first published work was a short story issued by The Ladder, the periodical released by the Daughters of Bilitis. The fourteen lesbian novels she wrote include All True Lovers, Tottie, A Flight of Angels, The Latecomer, and The Nesting Place.

She met legal secretary Muriel Inez Crawford in 1947. The couple was together for 57 years until Aldridge's death.

Aldridge died January 11, 2006, aged 94. She was awarded the Golden Crown Literary Society Trailblazer Award posthumously in June 2007.

Her first novel "The Latecomer" was reissued in 2009 in a 35th anniversary edition by A&M Books. In addition to the novel, editor Fay Jacobs collected essays from a vast array of lesbian icons attesting to Aldridge's lasting impact as an pioneer of early lesbian writing. This volume became the first of her work to appear in digital format in 2009.