Wagner began first shooting music videos and short films. In 2008, he began working regularly on television shows for BBC and ITV, and since then has been working almost exclusively for British and American film companies. His first role as a cinematographer for a TV show was for the 2008 BBC Three drama series Spooks: Code 9, for which he filmed all six episodes.
In 2017, Wagner became involved with the DClive-action adaptation of the Justice League, directed by Zack Snyder. The production was notoriously plagued with complications, most notably with the change of directors. During post-production, Snyder stepped down from the production following his daughter's death, with Joss Whedon stepping in to, not only complete the project, but also to redo the film entirely. Wagner wasn't involved on the reshoots conducted by Whedon, with Jean-Philippe Gossart taking over the role. Despite only 10% of his material being used in the theatrical cut, Wagner received sole credit for the film.
In 2020, after Warner Bros. decided to greenlit a director's cut of the movie, Snyder and Wagner were brought back to finish the film, using not only the existing and unused footage, but also filming additional material that hasn't been conceptualized before. The "Snyder Cut" (as referred by the media) was released on HBO Max in 2021.
