Other work
Marsters has narrated the audiobooks for The Dresden Files, a series of detective novels with a supernatural bent and the side short story collection in the same universe, Side Jobs, were also recorded by Marsters. He did not originally record the Dresden book Ghost Story due to a scheduling conflict, leaving fellow Smallville alumnus and actor John Glover to record it; this caused a fairly noteworthy public outcry by audiobook listeners. He returned for the following book Cold Days. On March 24, 2015, Jim Butcher announced that a new version of the Ghost Story audiobook was to be released on April 21, 2015, with Marsters returning as the narrator in response to fan demands.
In 2005, Marsters filmed a thriller, Shadow Puppets, with Jolene Blalock. Late that year, Marsters appeared on the television series Smallville playing Dr. Milton Fine—the popular Superman villain Brainiac—in eight episodes throughout the show's fifth season. He reprised his role as Brainiac in a four-episode arc in the seventh season, and did a cameo voice-over in season eight. He returned for one episode in the show's final season. On October 29, 2005, Marsters presented two performances of his own abridged adaptation of Shakespeare's Macbeth with American actress Cheryl Puente as Lady Macbeth, followed by question and answer sessions with the audience and acoustic concerts in London.
In September 2006, Marsters' interpretation of Godber's Teechers was performed on the Queen Mary with two other actors in Los Angeles. This is a play he had received critical acclaim for as a stage actor prior to his television work. Marsters co-starred in the 2007 cinematic release of P.S. I Love You alongside Kathy Bates, Hilary Swank, and Gerard Butler. Released in September 2007, Marsters starred in the direct-to-DVD animated film, Superman: Doomsday, providing the voice of iconic villain Lex Luthor. The film received mostly positive reviews.
In 2008, he guest-starred in Torchwood, a spin-off of the popular British science fiction television series Doctor Who, first appearing in the episode "Kiss Kiss, Bang Bang", as the nefarious omnisexual time traveller Captain John Hart. He reprised the role in the last two episodes of the second season.
He portrayed "Piccolo Daimao" in the live-action film adaptation of the popular Dragon Ball manga and anime, directed by James Wong and produced by Stephen Chow, which was released worldwide on April 10, 2009 and performed poorly both critically and financially.
On July 20, 2009, the film Moonshot aired on the History Channel in celebration of the 40th Anniversary of the 1969 Apollo 11 Moon landing. In this film, Marsters portrays Buzz Aldrin. On August 19, 2009, it was announced that he signed on for a role in Caprica as the terrorist leader Barnabas Greeley.
Also in August 2009, Marsters' science fiction western, High Plains Invaders aired on the Syfy Channel. In this alien invasion flick, Marsters portrays Sam Danville. It was announced in August 2010 that Marsters would be joining the cast of Syfy Channel series Three Inches as a series regular portraying Troy Hamilton, a former government agent who now leads a team of superheroes.
On June 24, 2011, Marsters appeared in an L.A. Theatre Works radio production of The Importance of Being Earnest, in the part of Sir John Worthing, which aired on June 25, 2011.
He has appeared on Supernatural in the episode "Shut Up, Dr. Phil", which aired October 21, 2011, alongside fellow Buffyverse co-star Charisma Carpenter. He also appeared in Warehouse 13 in 2013 as Bennett Sutton alongside fellow Buffyverse alumnus Anthony Stewart Head.
In 2018, some sources speculated that Marsters is the voice actor of Dragon Ball Super character Zamasu. In October 2021, at Fan Expo Canada, both Marsters and Dragon Ball Super voice director Christopher Sabat publicly confirmed that he voiced Zamasu under the pseudonym of David Gray. As a fan of the Dragon Ball franchise, Marsters agreed to play the role of Zamasu in Dragon Ball Super at the suggestion of Sabat himself and Sean Schemmel when they met during a convention. Marsters did so entirely for free in order to "redeem himself with the Dragon Ball Z community" after his appearance in the poorly received film Dragon Ball: Evolution.