At the young age of 13, in 1996 Isabeli made it to the finals of the Elite Model Look Contest when she was only 13. The following year Isabeli moved from Brazil to Milan, Italy, to begin her modeling career full time. In 1999, at the young age of 16, Isabeli appeared in the esteemed Victoria's Secret lingerie catalogue. Her appearance created a huge controversy as Victoria's Secret had earlier consistently stated that its strict policy was not to sign models younger than the age of 21 years old. However, the publicity from her appearance generated by this act proved beneficial to Fontana and Victoria's Secret and Isabeli quickly rose to fame. Just after the Victoria's Secret shoot, Isabeli was signed by Ralph Lauren, Versace, and Valentino. Isabeli has modeled for Marie Claire, Sports Illustrated Swimsuit Issue, ELLE and Vogue.
Isabeli was married to male model Alvaro Jacomossi but they divorced after a short marriage in 2002, the same year their son Zion was born. Isabeli next married model and actor Henri Castelli on December 10, 2005 and their son, Lucas, was born on October 23, 2006 in São Paulo, Brazil.
