Cornelia Meigs was born in Rock Island, Illinois, on December 6, 1884. Her parents were Montgomery Meigs, a civil engineer, and Grace Lynde Meigs. Meigs was the fifth daughter of six children. When she was one month old, her family moved to Keokuk, Iowa, where she lived a considerable part of her life.

Meigs attended Bryn Mawr College in Montgomery County, Pennsylvania, and graduated with an ABin 1908. After graduating, she taught English at St. Katharine's School in Davenport, Iowa, until 1913. While in Davenport, she wrote her first book, The Kingdom of the Winding Road, a collection of fairy tales. She frequently submitted short stories and plays for publication and wrote many of her books under the pseudonym Adair Aldon. In 1932, Meigs became a member of the English department at Bryn Mawr College, where she taught English composition and creative writing until 1950. She began as an instructor, became a professor of English, and then a professor emeritus. She also served as a civilian employee for the U.S. War Department in Washington, D.C., from 1942 to 1945.

Meigs was an acknowledged authority on children's literature. She was known for the many children's books she published at a time when literature geared specifically toward children was sparse. She wrote more than two dozen children's books, often with her students and twelve nieces and nephews in mind. Additionally, Meigs was a successful biographer—her book, Invincible Louisa: The Story of the Author of Little Women (1933), received critical acclaim for her sensitive portrayal of Louisa May Alcott. In 1956, she wrote a book about her alma mater entitled What Makes a College?: A History of Bryn Mawr.

Meigs received numerous awards throughout her extensive writing career. Her first award was a Drama League prize earned in 1915 for her play The Steadfast Princess (1916). In 1927, she won the $2,000 Beacon Hill Bookshelf Prize for The Trade Wind (1927). She also won three Newbery Honor Medals for Windy Hill(1921) in 1922, Clearing Weather(1928) in 1928, and Swift Rivers(1932) in 1933. Then, in 1934, at the annual conference of the American Library Association, she was awarded the Newbery Medal for her biography on Louisa May Alcott, Invincible Louisa: The Story of the Author of Little Women.

Meigs died at her home in Havre de Grace, Maryland, on September 10, 1973, at the age of 88.