Pseudonym for Robert Leslie Conly, an author who wrote books for children, primarily, though he wrote with a sophistication and creativity that is rare in many children's books. Though he wrote simply, he never talked down to the reader. This is likely because of his great sympathy and understanding towards children. Sally M. O'Brien said this of him: "He had a propensity and talent for dreaming. He could and did regularly create splendid imaginary worlds, with himself in dazzling, heroic roles. While all children do this to some extent, Robert O'Brien's fantasy world was so vivid that he still remembers the place and hour when he (by then a student in high school) made a solemn decision to give it up and to concentrate on living in the real world."
He was born January 11, 1918 in Brooklyn, New York to Leslie Marsland and Agnes O'Brien Conly. As a child, his family moved to Amityville, Long Island, where he grew up. He was a precocious child and had a talent in music, however he hated school and didn't get along well with his siblings. As editor for his high school's newspaper, his talent for writing emerged.
He entered Williams College in 1935, but dropped out during his sophomore year, at a time when doing so was not tolerated nearly so much. After a few months he decided that he wished to be a musician and attended various music schools for a time. A year later, his parents persuaded him to enroll at the University of Rochester and get his B.A. in English. Upon graduation in 1940 he decided to change his focus to writing.
From that time on he worked as writer or editor for various newspapers and magazines, such as Newsweek, the Washington Times-Herald, Pathfinder News and The National Geographic. He also had a family, consisting of his wife, Sally McCaslin, and four children: Christopher, Jane, Sarah and Catherine. He also had interest in music, reading, furniture making, and nature.
In the last ten years of his life he wrote four books, The Silver Crown (1968), Mrs. Frisby and the Rats of NIMH (1971), Report from Group 17 (1972) (his only book written for adults), and Z for Zachariah, published posthumously in 1975. He died March 5, 1973 at the age of 55 from a heart attack.
One of his daughters, Jane Leslie Conly, is also an author.