Bündchen was born in the Brazilian town of Três de Maio and grew up in Horizontina, Rio Grande do Sul. She is of German-Brazilian heritage from both her parents, Vânia Nonnenmacher, a bank clerk pensioner, and Valdir Bündchen, a university teacher and writer. She has five sisters – Raquel, Graziela, Gabriela, Rafaela and her fraternal twin Patrícia, Gisele's junior by five minutes. Bündchen is Roman Catholic and speaks Portuguese as her native language. She also speaks Spanish and English.
“ I was born in Horizontina, a town in the back-country of (Brazilian) state Rio Grande do Sul. The town was once mainly colonized by Germans. In the school which I attended, learning German was actually obligatory from third grade on. But being out of touch with the language for such a long time, I unfortunately forgot it. I belong to the sixth generation of my family in Brazil. ”
Originally, Bündchen wanted to be a professional volleyball player and considered playing for the Brazilian team, Sogipa. While in school, Bündchen was so thin that her friends used to call her "Olívia Palito" (Portuguese for Olive Oyl, Popeye's skinny girlfriend) and "Saracura" (a type of Brazilian shorebird).
In 1993, a then-13-year-old Bündchen joined a modeling course with her sisters Patrícia and Gabriela at her mother's insistence. The following year, Bündchen went to São Paulo on a school excursion to give them an opportunity to walk in a big city. In a shopping mall, while eating at McDonald's with her friends, Bündchen was discovered by a modeling agency. She was subsequently selected for a national contest, Elite Look of the Year, in which she placed second – Claudia Menezes, from Bahia, took first place. Bündchen placed fourth in the world contest, held in Ibiza, Spain. In 1996, Bündchen moved to New York City to begin her modeling career, debuting at Fashion Week.