His first professional job was for Rick Baker on Michael Jackson's music video for the song "Thriller". Gardner appeared in the video as the first zombie to crawl out of a grave as well as the hobbling zombie whose arm falls off. His daughter Brianna Gardner appeared in Shallow Hal (2001) as Cadence, the seven-year-old burn ward patient.
He was investigated by Arizona State Police and Missing Persons Bureau for the makeup effects work designed and created for the feature film Three Kings (1999).
His work on the 2010 Danny Boyle film 127 Hours received notoriety for the amputation sequences designed, engineered, and built to recreate the actual event in extreme closeup detail. The film's pre-release screenings at several film festivals have resulted in audience members requiring medical assistance. Gardner stresses though that the desired result was accuracy and an immersion in a recreation of the experience so that the audience experiences things through Aron Ralston's eyes.
Gardner is also noted for his work with electronic music duo Daft Punk. He helped create the signature robotic headgear worn by the duo. He was also involved in the music videos for their singles "Technologic", "Instant Crush", and "The Prime Time of Your Life", the latter of which he also directed. He worked alongside the duo as an associate producer for their first feature film Daft Punk's Electroma, a film that his company Alterian, Inc. also populated a world full of robots for.
Gardner's Alterian, Inc. designed and created the makeup effects for the film Jackass Presents: Bad Grandpa. The makeup effects for Johnny Knoxville's character were nominated for both an Academy Award for Best Makeup & Hairstyling and a Makeup Artist & Hair Stylist Guild Award in 2013. The work received the Guild Award for Best Special Makeup Effects in the Feature Film category.