Nancy Gray Larrick was born in Winchester, Virginia, on December 28, 1910, to Herbert S. and Nancy Nulton Larrick. She received her ABfrom Goucher College in 1930. After completing her undergraduate education, she taught in the Winchester public schools from 1930 to 1942. In 1937, while she was teaching, she received her MAfrom Columbia University, and in 1955, she received her EdDfrom New York University. During World War II she served as the education director for the war bond division of the United States Treasury Department.

In 1958, Larrick married Alexander L. Crosby, who was also a writer. In 1959, they co-authored a book—Rockets into Space. In the following years, which she spent in Pennsylvania, Larrick authored five books and edited one.

In 1964, she became an adjunct professor of education at Lehigh University in Bethlehem, Pennsylvania. She spent 15 years teaching at Lehigh, and when she was not at work, she lived in Quakertown in Bucks County. While at Lehigh, she wrote some of her most famous works.

Her first anthology was written in Pennsylvania, and several Pennsylvanian students helped her with choosing the selections. Larrick told Contemporary Authors Online, "I have edited eleven anthologies of poetry for young readers, and with each one I have turned to young readers for help in making selections. The first anthology I worked on was to be for second and third graders so I knew the poems had to be easy and interesting. At a school near Coopersburg, Pennsylvania, I borrowed groups of second and third graders whom I met twice a week for several months." She asked them which poems they could read, and which ones they would like to have in a book of their own. The children knew what they wanted. They recommended poems they called "real," and rejected poems they thought were "too sweet." The children also helped Larrick brainstorm ideas for a title. The title that the publisher had suggested did not appeal to the children at all, and they chose the title from a poem by William Blake called "Piper, Pipe That Song Again." The publisher listened to the children's suggestions and entitled the anthology Piper, Pipe That Song Again (1965).

During her years in Bucks County, Larrick also published many other works. Larrick also wrote frequently for periodicals. In 1965, she wrote an article for Saturday Review entitled "The All-White World of Children's Books," which criticized the racial biases of children's literature, calling attention to the omission of black characters in children's books. A study that analyzed trade books over a period of three years found that only four-fifths of one percent included contemporary black Americans. Additionally, when blacks were portrayed before World War II or outside of the United States, they were represented as slaves, menial workers, or sharecroppers.

In her written works, Larrick argued forcibly against racial stereotypes. She called the lack of racial equality in children's books one of the most critical issues in American education. She argues that the impact was destructive to black children and white children. Her works had a considerable effect on children's books. However, even now there has only been a slight increase in books that display regional, racial, and religious diversity, and various lifestyles in America's cultures.

Through her work as an educator, critic, editor, and anthologist of children's books, Nancy Larrick has been an influential voice in children's literature. Her work has earned her various awards, including the New York University Founder's Day Achievement Award in 1955, the Edison Foundation and the Carey-Thomas Awards in 1959, and the Certificate of Merit from the International Reading Association and the Drexel University Certificate for Contribution to Children's Literature in 1977. In addition, Larrick was inducted into the Reading Hall of Fame in 1977.

Nancy Gray Larrick died of pneumonia in Winchester, Virginia, on November 14, 2004.