Born in Putnam, Connecticut, Warner dreamed of being a famous author from the age of five. Her favorite book was Alice's Adventures in Wonderland. Being in a musical family, she was almost predisposed to play an instrument; in her case, she chose the cello, and her father bought her a cello kit at a young age. However, because of her frequent illness, Warner never finished high school. After leaving in her sophomore year, she learned from a tutor and finished her secondary education. In 1918, while she was teaching Sunday School, Warner was called to teach first grade, mainly because male teachers were being called to serve in World War I. She thought up the Boxcar Children while at home, sick. The stories were perfect for children, especially the majority (at least in her class) who did not speak English very well. She was criticized for depicting children with little parental supervision; her critics thought that this would encourage child rebellion. Her response was, however, that the children liked it for that very reason.
In 1924, The first book of what would much later become the series, was published. In 1942, this first book was revised and republished by another publisher, Scott Foresman, for use primarily in schools. In 1949, the 2nd book with the same characters was released (once again by Scott Foresman) but as a sequel to the first book. In 1950, the first book was re-released once again by Scott Foresman, and in subsequent years further books were published, finally turning it into a series more than 25 years after the first book was originally released. Albert Whitman became the sole publisher in the 1960s, until Scholastic also began publishing the series, only in paperback version around 1990, while Albert Whitman continued to publish in hardcover, as well as the same paperback format as Scholastic.
This lead to the series becoming far more popular than ever before due in part to Scholastic's inexpensive book club program in schools, updated cover artwork, and additional books being added to the series, written by ghostwriters. These more recent paperback printings are what people are currently most familiar with. Today, Albert Whitman & Company and Scholastic continue to publish the popular series. Other un-credited authors have contributed to the series starting with volume #20, adding more than 100 books to the series.
Before she passed away at age 89, Warner became a volunteer for the American Red Cross and assisted other charitable organizations.