Ward was born in Perth, Western Australia, as the second child of Gary and Claire Ward. Her older sister, Sophie Ward is also a model and she has younger twin brothers, Oscar and Henry Ward. She was educated at the Presbyterian Ladies' College, Perth and Shenton College.

As said herself in a Teen Vogue interview, she accompanied her friends to a modelling competition and ended up being scouted herself:

I had come straight from my auntie and uncle's farm, and I was wearing this big gray barn jacket with mud all over it. When the scout came up to me, I said, 'No, thank you.' But my friends were like, 'Hell, yes!' They forged my mum's signature [for mandatory parental consent], and pushed me in front of the cameras.

Ward didn't win the competition, but Vivien's Model Agency picked her up after seeing a small picture of her in an Australian magazine.

At only sixteen, Ward was the youngest model to be listed by American Vogue as one of the nine "It Girls" in the modeling world. She has been in shows for designers such as Versace, Gucci, Chanel, Valentino, Alexander McQueen, and many more. She also appeared in a Prada handbag advertisement, seen in magazines worldwide in Summer 2007. Ward has also graced magazine covers such as Vogue, W, and TIME Magazine's Style and Design issue. In September 2004, at the age of 16, Ward became the youngest fashion model on the cover of the American edition of Vogue and was the first model to appear on the cover of Teen Vogue magazine. She is the first model since Kate Moss to be the face for Calvin Klein's perfume "Obsession Night for Men" along with Philadelphia male model, Drew Keilt.

To date Ward's clients have included Balenciaga, Burberry, Calvin Klein, Christian Dior, Dolce & Gabbana, Hermès, Jean-Paul Gaultier, Jil Sander, Karl Lagerfeld, Louis Vuitton, Prada, Rochas, Swarovski, Valentino and Yves Saint-Laurent, and, altogether, Ward has appeared on 24 covers of Vogue magazine worldwide.

British photographer Nick Knight stated, "Gemma is one of the very, very few models who look as though they come from another dimension."Fashion designer Lazaro Hernandez of Proenza Schouler told Teen Vogue in February 2006 that, "She looked like no one else at the time. She was this alien, and fashion is always looking for newness." Her look inspired a new generation of baby doll-like models such as Vlada Roslyakova, Heather Marks, and Jessica Stam.

In Allure magazine (October 2006), Ward is described as "the model of the moment." Allure's creative director Paul Cavaco knows why: "We went through a period that was very va-va-voom, but now the pendulum has swung back. Gemma is ethereal, not earthy." Photographer Michael Thompson says, "She's an exotic blonde, the rarest of creatures."

Ward has long aspired to pursue acting and drama is a passion that she has held since she was a child. She has been cast in Australian director Elissa Down's upcoming film The Black Balloon also starring Toni Collette and Rhys Wakefield, as the girlfriend of a boy whose brother has autism. The Black Balloon had its world premiere at the Berlin International Film Festival in Germany in February 2008, where it received a Crystal Bear as the best feature-length film in the Generation 14plus category. She was also cast opposite Liv Tyler in the suspense thriller The Strangers as one of the three masked intruders. She also appeared in the music video for "Daughters" by John Mayer.

Ward appeared on the cover of the first issue of Vogue India; photographed by famed photographer Patrick Demarchelier. This is the second time Ward has appeared on an inaugural issue—the first time being the first-ever cover of Vogue China in 2005.

In July 2007, earning at an estimated total of $3 million in the past 12 months, Forbes named her tenth in the list of the World's 15 Top-Earning Supermodels.

Ward lives in New York and is close friends with fellow models Lily Donaldson, Caroline Winberg, Daria Werbowy, and Lily Cole.

In early 2008, Ward was reported to have been seeing actor Heath Ledger after media articles linked the two together at end of 2007 holiday celebrations. Ledger died shortly thereafter on January 22.

She can earn between $10,000 and $20,000 for a catwalk show and up to $100,000 for ad campaigns.

Represents Liano, Prada, YSL, Prada, Balenciaga, Lanvin, Hermès, Bulgari, Dior, Isetan, Jil Sander, and Versace

Is in the agency of IMG, the most Elite modeling Agency around with top models such as Tyra Banks, Gisele Bundchen and Heidi Klum.

Her sister, Sophie was a model, but stopped because she thought it was boring.

Shared an apartment with her best friend in New York City. Before she found an apartment she even slept on her friend's couch!

Her favorite movie is Almost Famous (2000).

Her favorite dogs are cocker spaniels.

Is a fan of Bob Marley.

One of her favorite places to visit is Sardinia.

Says her everyday look is a bit more scruffy than the clothes she models.

Wanted to be a actress when she was younger.

Her name means 'precious stone' in Italian.