In 1996, Bittar was registered by her mother in an Elite Model Management contest and subsequently joined the agency casting at only 14 years old. Her other agencies include Ford (New York, Miami), Women (Milan),[4] Select (London), Mega (Hamburg),[5] and Ten Model Management Agency, which is her mother's agency. In 2001, Bittar was nominated for the Abit Fashion Awards for the best female model. That same year, she participated in the São Paulo Fashion Week/Breast Cancer campaign at Alvo da Moda. She has walked for designers such as Alexander McQueen[6] and Ellus,[7][8] appeared in Victoria's Secret Fashion Show in 2003,[9] and has been photographed by Mario Testino.[1] As of 2016, was still modelling.[3] She has also hosted a TV show.[1][10]
^"Unknown". Arena (17–18). Emap Metro: 59. 2002. models Mariana Meckf Izabela Tavares, Paulo Ferreira, Felipe Ryan and Vinicius Costa at Elite, Fabiana Semprebom, Flavia Oliveira, Isabelli Fontana and Marcelle Bittar at Women, Katarina Scolla at Marilyn, Rafaela Pedro Falcao at IMG.
^"Sabrina Muller - Agence Mega". Officiel de la Couture et de la Mode de Paris (in French and Portuguese) (862–864): 93–94. 2002. Retrieved 30 January 2019.