McCarthy moved to Los Angeles where he slept on a couch in his sister's home before renting a Sunset Boulevard apartment for $500 a month. He soon formed the Alpha 60 Film Collective with fellow cinephiles Neil Matsumoto and Cecil Castellucci. Named for the fictional computer villain in Jean-Luc Godard's film Alphaville, the group collaborated on making numerous short films, which they showed at the Echo Park Film Center. McCarthy's 12th film for Alpha 60, entitled Maid, was envisioned as a Spanish language documentary that evolves into a Korean musical in under six minutes. Upon seeing the short, a scout from the Sundance Film Festival recommended McCarthy submit any subsequent work to Sundance. This vote of confidence prompted McCarthy to make "Cry for Help," a short film about a zombie version of Jesus Christ, which premiered at Sundance in 2005. His next short film, Chinese Box starring Sam Ball and Petra Wright, was shot for just $300 and played at Sundance in 2009. Each film toured the festival circuit and netted interest from producers, but no offers for further production. His third short to play at Sundance, an 11-minute ghost story called The Pact, debuted in 2011. When the short was optioned for a longer production, within six weeks McCarthy expanded it into a feature and was contracted to direct the new feature-length version of the film. The 89-minute feature of The Pact premiered at Sundance in 2012 and was picked up for distribution by IFC. A wide release in the United Kingdom grossed $4 million, and the film was well received stateside with the Los Angeles Times later calling it "a crisply made haunted house movie that benefited from its grab-bag approach." McCarthy immediately got to work on his next film, originally titled Home, which premiered at Austin's South by Southwest Film Festival in 2014. Before distribution, McCarthy changed the film's name to At the Devil's Door at IFC's suggestion. That same year McCarthy served as executive producer on a sequel to The Pact starring the first film's original leads, but written and directed by Dallas Hallam and Patrick Horvath. McCarthy had no creative involvement with the sequel. McCarthy was approached by French horror film directors Julien Maury and Alexandre Bustillo to make an English language version of their film Livid, but the project fell through. In 2016 McCarthy was featured as part of the 17-disc Blu-ray set Feast,