Lily Monica Donaldson is the daughter of photographer Matthew Donaldson and wife Tiffany.

Donaldson was born in London, and educated at the Camden School for Girls, living in Kentish Town with her parents.

Since being scouted by Select Model Management in 2003 at the age of 16 while shopping in Camden, Donaldson has become one of Britain's most coveted models, landing campaigns for leading fashion houses such as Dior, Jil Sander, Burberry and Dolce & Gabbana.

In the May 2007 issue of American Vogue, she was featured on the cover with fellow models Doutzen Kroes, Caroline Trentini, Raquel Zimmermann, Sasha Pivovarova, Agyness Deyn, Coco Rocha, Hilary Rhoda, Chanel Iman, and Jessica Stam as the new crop of supermodels and she was described as the "smartest and most sophisticated of the bunch". Later, in the September 2007 issue of British Vogue, she was named a "Head Girl", a model to watch out for in the upcoming season. Lily has appeared on the cover of British Vogue twice, Italian Vogue, Vogue china and Australian Vogue to name a few. Whilst on the cover of the March 2009 issue of the UK Vogue she was also on the Australian Vogue and Italian Vogue cover.

Donaldson has appeared in advertisements for Gucci, Chanel, Balenciaga, Christian Dior, Dolce & Gabbana and Jil Sander, Roberto Cavalli, Valentino, Emanuel Ungaro, Max Mara as well as being the face of British luxury goods house Burberry. She is one of the favorite models of designer Alber Elbaz of Lanvin. Booking agents describe her as down to earth and a pleasure to work with.

Donaldson has walked for: Alexander McQueen, Anna Sui, Calvin Klein, Chanel, Chloé, Dior, Diane von Furstenberg, Dolce & Gabbana, Donna Karan, Fendi, Giorgio Armani, Gucci, Hermès, Jil Sander, John Galliano, Karl Lagerfeld, Lanvin, Louis Vuitton, Marc Jacobs, Michael Kors, Missoni, Prada, Oscar de la Renta, Ralph Lauren, Roberto Cavalli, Rochas, Stella McCartney, Tommy Hilfiger, Valentino, Vera Wang, Versace, Vivienne Westwood, Yves Saint Laurent, Zac Posen and many more.

In 2009 she became the face of Burberry and Gucci; she also appears on the cover of British Vogue in March.

Donaldson dated Vladimir Restoin Roitfeld, son of Vogue Paris Editor-In-Chief Carine Roitfeld.

She is close friends with models Gemma Ward and Irina Lazareanu, the latter with whom she shot a Mulberry campaign.Her other friends include fellow models Freja Beha Erichsen, Caroline Winberg, Lisa Cant, Jessica Stam, Caroline Trentini, Julia Stegner, Agyness Deyn and Raquel Zimmermann.

In May 2008, Donaldson reportedly spent US$2.2 million on purchasing a two-bedroom apartment on Tompkins Square Park around East Eighth Street in New York.