Born Catherine marie-Agnes de Saint Phalle on October 29 at Nevilly-sur-Seine, France, the second of five children of Jeanne Jacquiline nee Harper and Andre Marie-Fal de Saint Phalle. Her father is one of seven brothers sharing ownership in the family's banking house and directs New York operations. When the stock market collapses, he loses both his share of the business and his entire fortune. Sent to live with paternal grand-parents in Nievre, France, where she spends the next three years.
Returns to parents' home, now in Greenwich, Connecticut. Spends summer holidays in France with maternal grandfather, a prominent American lawyer in Paris, at his Chateau de Filerval(with formal gardens designed by Le Notre).
Family moves back to New York City. Marie-Agnes, now known as Niki, attends the Convent School of the Sacred Heart. Upon expulsion, sent to Princeton, New Jersey to live with maternal grand-parents who left France shortly before World War II. Returns to New York City and attends Brearley School in New York City where she befriends Jackie Matisse, daughter of prominent gallerist Pierre Matisse. Matisse will later create glass containers for sacred waters at Niki's Tarot Garden. Reads Edgar Allan Poe, Shakespeare and Break tragedy, takes part in school performances and writes first poems and plays. In 1944, leaves Brearly after applying red paint over the fig leaves placed on the Greek sculptures adorning the grounds. Attends another convent school in Suffren, New York and eventually graduates in 1947 from Oldfields School in Maryland.
Starts a career as a fashion model. Photographs appear in Vogue, Harper's Bazaar, Elle, Life and other French and American magazines. At 18, elopes with Harry Mathews whom she has known since early adolescence. Moves to Cambridge, Massachusets in 1950. Produces her first oils and gouaches while husband studies music at Harvard University. First child Laura is born in Boston in 1951.
Moves to Paris and studies theater and acting while husband takes music classes at L'Ecole Normal de Musique. Spends summer months in the South of France, Spain and Italy visiting museums and cathedrals. Hospitalized in Nice with a nervous breakdown. Finding that painting helps her to overcome this crisis in her life, decides to give up acting and become an artist. Around the same time, husband abandons his music studies and begins his first novel (later he will bound the literary magazine Locus Solus).
Couple returns to Paris where they share a house with Anthony Bonner, an American jazz musician and composer. Introduced to American painter, Hugh Weiss, who becomes a mentor and encourages her to continue painting in her self-taught style. Moves to Deya on the island of Mallorca where son Philip born in 1955. Visits Madrid and Barcelona, where she discovers the work of Gaudi and is deeply affected by the experience, opening her to the many possibilities for using diverse materials and found objects as structural elements in sculpture and architecture. Returns to Paris and meets jean Tinguely and his wife, Eva Aeppli. Asks Tinguely to weld armature for her first sculpture.
Lives in Lans-en-Vercors in the French Alps with family. First solo exhibition of paintings in St. Gallen, Switzerland in 1956. Paints and explores various collage elements.