Margaret Ayer Barnes was born in Chicago, Illinois, to a family that took a keen interest in civic affairs. Her older sister Janet Ayer Fairbank became a well-known suffragist and writer. Margaret graduated from Bryn Mawr with a bachelor's degree in English and philosophy in 1907. In 1910, she married Cecil Barnes, a prominent Chicago lawyer, with whom she had three sons. During these years, she served as alumnae director of Bryn Mawr and helped organize the Bryn Mawr Summer School for Women Workers in Industry. In 1926, at age 40, her life changed dramatically when she was in an auto accident while vacationing in France and suffered a broken back, skull, and ribs. During her slow recovery, she took up writing with the encouragement of Edward Sheldon, a playwright whom she had met as a child. Between 1926 and 1930, she wrote several short stories and three plays, including a highly successful 1928 play adapted from Edith Wharton's novel The Age of Innocence. In 1931, she won the Pulitzer Prize for her first novel, Years of Grace. Over the next eight years, she published four more novels, including Westward Passage (1931) and Edna His Wife (1935).