Harlow was born in Oshawa, Ontario, the daughter of Sandi Herbert and David Harlow. Though her mother named her Shalom, meaning "peace" in Hebrew, her family is not Jewish. She was discovered at a Cure concert in Toronto and started modeling straight out of high school.[citation needed] She has since appeared on numerous magazine covers, editorials, and top runway shows, and appeared in movies and co-hosted MTV's House of Style with fellow supermodel Amber Valletta. She was the long-time favorite model for many designers who found that her look translated well between commercial and couture. She is the first ever winner of Vogue/VH1's Model of the Year Award. Harlow is the spokesperson for Chanel's Coco fragrance. She has two younger brothers, Chris and Nathan.

In July 2007, earning at an estimated total of $2 million in the past 12 months, Forbes named her thirteenth in the list of the World's 15 Top-Earning Supermodels.

In 2007 she modeled for Jones New York, Tumi, Tiffany & Co, Nautica, and Chloé. The following year, she appeared in the Valentino Spring/Summer 2008 campaign.

Most recently she featured as the only model in a digital catwalk for Viktor & Rolfs Spring/Summer 2009 show.

She currently lives in Brooklyn, NY and dates the resin artist Dustin Yellin.[citation needed]