Gandy began modeling in 2002 after winning a daytime-TV model search competition (organized by Richard and Judy). At the time he had a job delivering cars to a car magazine. Gandy then signed with Public Image Worldwide, modeling mostly for catalog work in the UK market before making top model status for Dolce & Gabbana. He has appeared in numerous campaigns and catwalk shows for the luxury brand and has worked with supermodels such as Gemma Ward and Naomi Campbell . He is best known for his advert with Dolce & Gabbana's fragrance "Light Blue" which had 11million online hits and saw a 50 ft poster of him grace Times Square. He also modeled for the luxury brand's 2008 calendar, shot by top photographer, Mariano Vivanco. He returned to become the face of the second Light Blue fragrance campaign for 2010.
Other campaigns he's worked for include: 7 for all Mankind, Shiatzy Chen, Zara, Ermenegildo Zegna, and Stefanel. He also appeared on covers for VMan and L’Optimum and editorials for Harper's Bazaar and Spanish Glamour. In November of 2011, he appeared on the cover of Details (magazine) which was shot by photographer Norman Jean Roy. On 26 June 2009, Forbes Magazine ranked Gandy as the world's third most successful male model, behind Matt Gordon and Sean O'Pry.
Gandy was interviewed on Friday Night with Jonathan Ross which was aired on 30 April 2010 and is a regular blogger for Vogue magazine's website. In August 2010 it was reported he had begun an acting career by making a short film with Helena Christensen.
Gandy currently writes a blog for Vogue where he discusses his modelling and extra-curricular work such as his love for cars, February 2011.
Gandy is currently ranked #8 in the list of "Money Guys" on models.com.
He is currently signed to DNA Model Management in New York City and Select Model Management in London.