Cooney was born on 6 August 1917 in Room 1127 of the Hotel Bossert in Brooklyn, New York, to Russell Schenck Cooney (a stockbroker) and Mae Evelyn Bossert (a painter). She had a twin brother and two younger brothers. She attended Buckley Country Day School and later Boarding School.
She later graduated from Smith College with a history degree, and her first book illustrated, Ake and His World, by the Swedish poet Bertil Malmberg, was published a year after graduation. During World War II, she served in the Women’s Army Corps. Soon after her service, she met and married Guy Murchie(Jr), in 1944 and had two children (Gretel and Barnaby.) She later divorced, and remarried Charles Talbot Porter in July 1949 and had two more children (Charles and Phoebe.)
Ten years later, she won her first Caldecott for Chanticleer and the Fox , a book that she illustrated and adapted the text from Chaucer. Between then and when she picked the other Caldecott in 1980 for Ox-Cart Man (written by Donald Hall), she traveled a lot, picking up ideas to draw and, occasionally, write. In 1983 she and Miss Rumphius won the National Book Award in category Picture Books (split with William Steig and Doctor De Soto).
In 1996, Maine Governor Angus King honored Miss Cooney by proclaiming the day "Barbara Cooney Day". Her last book, Basket Moon, was published six months before her 10 March 2000 death at a house that her son built for her in Damariscotta, Maine.
Portions of her original artwork are being displayed at Bowdoin College.