Born on August 12, 1955, Ann Martin grew up in Princeton, New Jersey. Her father, Henry R. Martin, worked as an artist and cartoonist while her mother, Edith Matthews Martin, taught preschool. Both parents enjoyed fantasy and children's literature, and they provided an imaginative home in which Ann and her little sister, Jane, could grow, play, and daydream. The Martins enjoyed reading aloud together, and Ann liked to make up stories of her own—never dreaming that someday she would be an author.

Martin attended Smith College, spending summer vacations as a therapist working with autistic children. After graduating cum laude in 1977, she acted on her childhood desire to be a teacher and taught for one year at Plumfield School in Noroton, Connecticut. She enjoyed teaching, but she soon realized that she wanted to be involved in some manner with children's books. The following year she entered the publishing profession, serving as an editorial assistant for the Archway Paperbacks division of Pocket Books in New York City from 1978 to 1980. Soon, Martin was writing seriously, and at the same time she quickly moved up the ladder as copywriter for Teen Age Book Club, Scholastic Book Services (1980-1981), associate editor (1981-1983), and editor (1983); senior editor of Books for Young Readers at Bantam Books (1983-1985); and finally writer and free-lance editor (since 1985).

An extremely prolific and disciplined author, Martin considers writing both an indulgence and a creative outlet. While imagination is essential to her writing, memory is equally vital. As she says in Something about the Author, "One of the most important tools I use in my writing is my memory. . . . It's just as important to be able to transport oneself back to childhood as it is to have a vivid imagination, in order to write believable children's books." She clearly remembers the significant as well as the trivial events and emotions of her life from early childhood onward. She also draws on her experiences as a teacher and editor and her interest in child psychology and learning disabilities for her writings.

Martin is most famous for The Baby-Sitters Club and Baby-Sitters Little Sister books which have earned her an international reputation as one of the most popular writers for elementary and middle-school-age girls. While the idea for The Baby-Sitters Club was not her own, having been suggested to her by Scholastic's Editor-in-Chief Jean Feiwel, Martin developed the characters and situations for the entire series. Originally intended as a series of four volumes, the list of titles has expanded to more than forty, with another ten plus in the Little Sister series. Although the bulk of her time is spent on these two series, she still manages to write at least one hardcover novel each year.

The author stays in touch with youngsters through contact with her friends' children, her fan mail, and visits to schools. She participates in the Adopt-a-School Program of the National Dance Institute, sponsoring New York's P.S. 2 in Jacques D'Amboise's inspirational program for inner-city school children.

Martin is an animal lover, and that passion comes across in many of her books. Her love of horses and horseback riding is evident in Me and Katie (the Pest), and many of her fictional families own pets. Martin has a particular fondness for cats, which often are included in her books. She has never married, but lives in New York City with her cats, Rosie and Mouse (not coincidentally the name of one of the O'Hara family pets in With You and Without You).