When she was thirteen, in 1994, Mariana debuted on television in the telenovela 74.5 - Uma Onda no Ar in Rede Manchete making a cameo appearance to the latter. Shortly afterwards, she was invited to join the cast of Fascinação of SBT in 1998, where she played the character Emília, her first major television role. In the same year, she joined Rede Globo and began working in her (Rede Globo) productions. She appeared in the episode "Dupla Traição" in the series Você Decide and in the film Caminho dos Sonhos portraying the character Ruth Stern. She also participated in the pilot of the series Sandy & Junior portraying the character Vicky.
In 1999, she played Celi Montana in Andando nas Nuvens. She also made a cameo appearance in the telenovela Força de um Desejo playing Ângela, in 2000.
Mariana played the character Bionda, which yielded great success for her career. She later starred in the film Xuxa Popstar.
In 2001, she appeared in Brava Gente in the episode, "A Sonata", playing the character Luciana. She first performed in the Portuguese voice over translation for the character Sharon Spitz in the Canadian/Chinese animated series Braceface. She later did some ads for Fox Kids Brazil and she also played Izabel de Avelar in A Padroeira. That same year, she also starred in her second film, Dias de Nietzsche em Turim, playing Júlia Fino.
