Gigi Perreau achieved success as a child actress in a number of films, including Green Dolphin Street (1947). She played the daughter ofClaude Rains and Bette Davis's characters in the 1944 film Mr. Skeffington (1944). In Shadow on the Wall (1950), she starred as the sole witness to a murder. As the "top child movie actress for 1951", the then ten-year-old was given the keys to the city of Pittsburghby its mayor, David L. Lawrence, the youngest to be so honored.
However, her career lost momentum as she grew up. In 1959, she played a friend of character Mary Stone (Shelley Fabares) on ABC's The Donna Reed Show. That same year, she had a supporting role in the sitcom The Betty Hutton Show on CBS, with her older brother Gerald. In 1960, Perreau was cast as Julie Staunton in the episode "Flight from Terror" of the ABC adventure series, The Islanders, set in the South Pacific. She was cast in two episodes, "Don Gringo" (1960) and "The Promise" (1961) of the Nick Adams' ABCwestern series, The Rebel.
In 1961, she played Mary Bettelheim in the episode "The Twelfth Hour" of the ABC/Warner Brothers television crime drama, The Roaring 20s. She was cast in a recurring role on ABC's Follow the Sun series from 1961–1962 as a secretary, Katherine Ann "Kathy" Richards. She guest starred on The Rifleman in 1960 and 1961. She made two guest appearances on Perry Mason: in 1958 as Doris Bannister in "The Case of the Desperate Daughter" and in 1964 as Phyllis Clover in "The Case of the Sleepy Slayer." On October 11, 1960, Perreau and Robert Harland were cast as Sara Lou and Lin Proctor, a young couple from the east who have eloped and are heading west in the second episode, "The Land Beyond", of ABC's Stagecoach West, with Wayne Rogers and Robert Bray. In 1970, Perreau appeared on The Brady Bunch as a teacher Greg Brady has a crush on. In the new millennium, she provided a voice in the animated film Fly Me to the Moon, and is credited by the Internet Movie Database with two other movies in post-production.
Perreau is an alumna of Immaculate Heart High School in Los Angeles and has taught drama classes there. As of 2010, she is a member of the board of directors of both theDonna Reed Foundation for the Performing Arts and the Will Geer Theatricum Botanicum and is the vice-president of the Drama Teachers Association of Southern California.
On February 8, 1960, Perreau was awarded a star on the Hollywood Walk of Fame for her work in television.
On March 14, 1998, she was honored by the Young Artist Foundation with its Former Child Star "Lifetime Achievement" Award recognizing her outstanding achievements within the entertainment industry as a child actress
Perreau's elder brother Gerald (stage name Peter Miles) and, to a lesser extent, her younger sisters Janine and Lauren, also had a measure of success in film and on television. Perreau married Emil Frank Gallo, an East Coast financier in 1960 with whom she has two children: Gina Maria Gallo Paris and Robert Anthony Gallo, a heavy metal and rockguitarist. They divorced in 1967. She also wed Gene Harve deRuelle in 1970 and bore two additional children, Danielle deRuelle and Keith deRuelle. Her second marriage ended in 2000.