Giselle was born in Brazil to a family of German origin, her mother Vânia was a bank clerk and her father Valdir was a university teacher and writer. She is one of six girls. Her sisters are: Raquel, Graziela, Gabriela, Rafaela and her twin Patricia. She had a long-term relationship with Leonardo DiCaprio. Among her boyfriends were the model Scott Barnhill, the Brazilian billionaire Joao-Paulo Diniz, and the actor Josh Hartnett.