Marianne Thieme studied at the Duno College in Doorwerth. After that she studied from 1991 to 1992 at the Sorbonne in Paris, France. From 1992, she studied Dutch Law at the Erasmus University Rotterdam with a specialization in administrative law. During this time she became a vegetarian. Her interest in animal rights motivated her to start studying law. Thieme graduated in 1997.
From 1998 to 2001 Marianne Thieme worked at research agengy B&A Group in The Hague. Between 2001 and 2004 she was policy official at Bont voor Dieren (Fur for Animals, a Dutch anti-fur animal welfare foundation). Until November 2006 she was the general manager of Stichting Wakker Dier (a Dutch animal welfare foundation against industrial agriculture).
In February 2004 she was nominated to become the party's lijsttrekker (party leader) for the European Parliament election of 2004. This time the party gained 153.000 votes (3,2%), three times as much as in 2004. The number of votes was not enough to obtain a seat in the European Parliament.
During the Dutch general election of 2006 the Party for the Animals gained 179,988 votes (1,8%), enough for two seats in the Dutch parliament. The party became the world's first party to gain parliamentary seats with an agenda focused primarily on animal rights.
She became a Seventh-day Adventist in 2006 "because [it is] a church with compassion and care for our planet."
In May 2004 her book De eeuw van het dier (The century of the animal) was published. In this book animal rights are at the centre point. A line is drawn from the end of slavery through women's liberation to animal rights.