Zimmermann was discovered by a scouting agency in Porto Alegre, Brazil at the age of 14 and made her way to Japan and on to Paris. Shortly thereafter, Steven Meisel booked her for the cover of Vogue Italia, September 2000, and her modelling career began in earnest.
Zimmermann has campaigned for such brands as: Balenciaga, Bloomingdales, Cavalli jeans, Cerruti, Chanel eyewear, Chloé, Christian Dior, CK by Calvin Klein, Clairol, Dolce & Gabbana, Dsquared, Emanuel Ungaro, Escada, Fendi, GAP, Gucci, Giorgio Armani, H&M, Hermès, Hugo Boss, Louis Vuitton, Lanvin, MAC Cosmetics, Max Mara, Neiman Marcus, Prada, Roberto Cavalli, Shiatzy Chen, Valentino, Versace, and appears regularly in American Vogue, French Vogue, Italian Vogue, W, Harper's Bazaar, Visionaire, POP and Self Service. She also appeared in the 2002, 2005 and 2006 Victoria's Secret fashion shows.
Zimmermann has appeared on many magazine covers, such as: Vogue (Brazil, USA, Italy, France, Japan, China, Greece, Germany, Russia), Harper's Bazaar, Elle, Numéro, L'Officiel, Marie Claire, i-D, V and French.
In the May 2007 issue of American Vogue she was featured on the cover with fellow models Doutzen Kroes, Caroline Trentini, Hilary Rhoda, Sasha Pivovarova, Agyness Deyn, Coco Rocha, Jessica Stam, Chanel Iman, and Lily Donaldson as one of the "World’s Next Top Models." In 2008 casting agent James Scully, who is responsible for picking which model is to score a spot on top runways, says in regard to Zimmermann:
The energizer model! I think she's the only model of the last ten years who never goes out of fashion. It's as though she never ages yet gets better-looking each season. Probably the most versatile model of all, she truly could be in any show. Her professionalism rivals any model and her timeliness is equal to Cindy Crawford's, whose punctuality was legendary.
In 2007 Zimmermann appeared on the cover of V and in the first ever television commercial by Gucci for its new fragrance, Gucci by Gucci directed by David Lynch.
Zimmermann was ranked number one on international model ranking website models.com from December 2007 until February 2010. As of April 2011 she is, because of her long run on the Top 100, ranked 14 on the Top Model Icons of All Time list. She has recently been featured in the H&M, Fendi, Lanvin, Printemps and Roberto Cavalli advertising campaigns. Zimmermann appeared on covers of the June 2008 issue of Elle Brazil, the July 2008 issues of Vogue Nippon and Numéro Tokyo and the cover of the August issue of Chinese Vogue, as well as the covers of the Vogue Nippon issues from December 2008 and October 2009. She was the face of Oscar de la Renta for the spring/summer 2009 advertising campaign photographed by Craig McDean as well the face of Marc Jacobs for the 2009 spring/summer campaign photographed by Juergen Teller.
The May 2009 issue of American Vogue featured her as one of the faces of the season, alongside Liya Kebede, Lara Stone, Natasha Poly, Caroline Trentini, Jourdan Dunn, Natalia Vodianova, Anna Jagodzinska, and Isabeli Fontana.
Vogue Paris declared her one of the top 30 models of the 2000s.
She starred in the Lady Gaga music video for "Born This Way", where she was featured wearing designer clothing and helped give birth to a non-prejudice race from the "Mother Monster"
Zimmermann, a German Brazilian, was born in Bom Retiro do Sul, RS, Brazil. She reports that she practices the Transcendental Meditation technique.