Joan Winsor was born on Dec. 9, 1928, in New York, N.Y. She enjoyed reading and writing from an early age and as a teenager wrote a short story for a national magazine. She majored in physiology as an undergraduate at Vassar College in the late 1940s and completed graduate studies in psychology at City College in the mid-1950s. She married Peter Blos, Jr., in 1953.

Blos's interest in language, child development, and children's literature led her to a variety of educational and research positions at several institutions, including writing primers while working in the publications division of Bank Street College of Education. She ventured into picture books by collaborating with Betty Miles on writing ‘Joe Finds a Way' (1967) and ‘Just Think!' (1971). Among her other picture books were ‘ “It's Spring,” She Said' (1968), ‘Martin's Hats' (1984), ‘Old Henry' (1987), ‘The Grandpa Days' (1989), and ‘Lottie's Circus' (1989).

‘A Gathering of Days: A New England Girl's Journal, 1830–32' received both the Newbery Medal and the American Book Award in 1980. The historical novel stays true to place and time while using diary entries to chronicle the thoughts and feelings of a 14-year-old girl as she deals with a new stepmother, the death of a friend, and other events. The book grew out of Blos's interest in the history of New Hampshire that began when she started doing research on an old farmhouse purchased by her husband's family.

Some characters in Blos's second work of historical fiction, ‘Brothers of the Heart: A Story of the Old Northwest, 1837–38' (1985), are linked to the heroine of her first novel through friendships and familial lines. The story itself, however, is set in Michigan and uses flashbacks to tell the tale of a lame boy's progression towards maturity during a dangerous trading expedition. Blos's other works included the picture books ‘Martin's Hats' (1984) and ‘Old Henry' (1987) and the novel ‘The Heroine of the Titanic' (1989).