Louise Fitzhugh was born in Memphis, Tennessee on October 5, 1928. She was the only child of attorney Millsaps Fitzhugh and Louise Perkins. After attending an exclusive girls' school, Miss Hutchison's, she attended three different colleges but never obtained a degree, and traveled in Europe, before finally settling down in New York City to pursue a career as a painter. In the late 1950s she and a friend, Sandra Scoppetone, began work on a beatnik parody of Kay Thompson's Eloise, which was published in 1961 as Suzuki Beane. In 1964 she published her first novel, Harriet the Spy. Although it received mixed reviews from adults at the time, today it is widely regarded as a forerunner to the sort of realistic children's fiction that would dominate the late 1960s and 1970s. Two novels about Harriet's friends followed: The Long Secret in 1965 and Sport, published posthumously in 1979.
Contemporary social issues figured prominently in much of Fitzhugh's work for children: Bang Bang You're Dead was a 1969 picture book with a strong anti-war message and Nobody's Family Is Going to Change (1975) explored both women's rights and children's rights. Ironically, it became the basis of the Broadway musical The Tap Dance Kid with the book's minor male characters taking a lead role, thereby completely overshadowing Emma, the female protagonist. Needless to say, this happened after Fitzhugh's untimely death in 1974 at the age of 46. After her death, three picture books were also published: I Am Three, I Am Four, and I Am Five.