Mills has also been featured in advertisements for Tommy Hilfiger, Michael Kors, and Gap Inc. Models.com has called him "one of the most sought after names in the industry.

In 2004, Mills made his debut as a runway model for the fall Gucci and Yves Saint Laurent collections in Milan and Paris.

In 2009, Mills appeared in the naked Dolce & Gabbana Anthology Fragrance campaign with a number of other established models including Claudia Schiffer, Naomi Campbell and Tyson Ballou.

Mills became one of the models to star in Lacoste's "new look" campaign in January 2011, a different advertising concept under the new tagline, "Unconventional Chic".

[11] In 2011 and 2012, Mills appeared in the CBS sitcom 2 Broke Girls, playing the role of Robbie, Max's (Kat Dennings) boyfriend.

Mills plays Sean, who comes home after serving a five-year prison sentence and must contend with "the remains of a life interrupted.

[19] In 2021, Mills was selected to play the supporting role as Jesse in the CBS crime drama series NCIS: Hawaiʻi.