Eleanor Rosenfeld Estes was born on May 9, 1906, in West Haven, Connecticut, to Louis and Caroline Gewecke Rosenfeld. Her father died when Estes was a child, and her mother worked as a dressmaker. Estes has credited her parents with instilling in her a love of books. She has cited as another important early influence her mother's skill at dramatic storytelling and her extensive repertoire of folktales, songs, and anecdotes. Estes always wanted to be a writer, although she never set out to write for young adults.

Her own childhood provided an appropriate storehouse of ideas and experiences. Estes and her sister and two brothers were raised in West Haven, which she has described as a "perfect town to grow up in," because it offered an appealing mix of small town and country life. West Haven appears in the Moffat books and in Ginger Pye as the fictional town of Cranbury.

After graduating from high school, she went to work in the children's department of the New Haven Free Public Library, where in 1928 she became the children's librarian. In 1931 she won a Caroline M. Hewins scholarship for children's librarians to the Pratt Institute Library School in New York City. In 1932 she married a fellow student, Rice Estes, later a professor of library science and director of the Pratt Institute Library. In that same year she began working in the children's department of the New York Public Library. When her first book, The Moffats, was accepted for publication in 1940, she left the library to write full-time.

The Middle Moffat, Rufus M., and The Hundred Dresses were named Newbery Honor Books. Ginger Pye won the 1952 Newbery Medal, as well as the 1951 New York Herald Tribune Festival Award. Although Ginger Pye is generally considered to be a lesser achievement than the author's earlier works, the enduring popularity of the Pye family and Ginger, their "intellectual" dog, resulted in the appearance of a sequel, Pinky Pye.

Estes continued to publish books that were well received by both young readers and critics. The prolific author wrote fifteen books for children, as well as an adult novel and numerous magazine articles. She died on July 15, 1988, in Hamden, Connecticut.