Kerr was born in Sydney but raised in Gunnedah, New South Wales, a small rural town in Australia. Her parents are Therese and John Kerr, and she has a younger brother named Matthew. According to the Australian a current affair program 'Today Tonight' she is of mixed ethnic heritage, these are Iranian, Serbian, Turkish and Filipino combined. During her childhood, Kerr stated she 'raced motorbikes and rode horses on her grandmother's farm' and describes her early life in the Australian countryside as 'very grounding ... there wasn't any pretentiousness and no one really cared what you were wearing. You could just be you.
At age thirteen, Kerr entered and won the 1997 annual "Dolly Magazine"/"Impulse Model Competition". She was flown to Sydney a week before her fourteenth birthday to shoot for the magazine. Upon Kerr's win, local media expressed 'concerned outrage' at her young age. The controversy raised concerns about the glorification of young girls within the fashion, beauty, and entertainment industries. Some conservative media outlets claimed her "Dolly" shoot (including images of fourteen year old Kerr in bathing suits) constituted a form of child pornography. Of the press, Kerr said: 'In the media at the time they were trying to cling on to anything remotely to do with paedophilia. Dolly is a magazine for teenage girls, not for old men. And I was fully clothed! Doing a winter shoot! They just made something out of nothing.'
Once in New York, Kerr had a multitude of runway appearances, and then signed with Next model agency in early 2004. From there, she was immediately booked for runway and print campaigns for dozens of major labels, including Baby Phat, Lisa Ho, Voodoo Dolls, Levi's, Bettina Liano, Nicola Finetti, L.A.M.B, Heatherette, Betsey Johnson, Trelise Cooper, Jets, John Richmond, Blumarine Swimwear, Neiman Marcus, Seafolly Swimwear, Anna Molinari, Rock and Republic and Roberto Cavalli.
In 2006, Kerr broke into the United States market when she signed a lucrative cosmetics contract with Maybelline New York. The campaign ran in a series of internationally sold women's beauty magazines, including "Cosmopolitan", "CLEO" and "ELLE", and was eventually featured in Victoria's Secret catalogues.
Following her success with Maybelline, Kerr became the first Australian model to be offered a contract with Victoria's Secret and upon her acceptance, the first ever Australian Victoria's Secret Angel. She became a featured model on the company's internationally-accessed website, joining the stable of prestige models already signed to the lingerie giant including Gisele Bündchen, Alessandra Ambrosio, Karolína Kurková, Adriana Lima, Selita Ebanks, and Heidi Klum. Kerr's increasing popularity as one of the globally recognized Angels led for Kerr to be featured in the Victoria's Secret 2006 and 2007 televised runway shows, which aired on four continents.
As of 2007, Kerr has signed as the face of Californian fashion retailer Arden B. After debuting in their Spring and Summer ad campaigns, Kerr returned for their Fall 2007 campaign, shot by fashion photographer Diego Uchitel. She has also become the new face of Clinique "Happy", and signed a lucrative six-figure deal to be the new face of Australian department store David Jones, replacing model Megan Gale. In 2008, earning at an estimated total of $3.5 million in the past 12 months, "Forbes" placed Kerr tenth in the list of the world's top-earning models.