C. Robert Cargill

The idea for his first film came to fruition when he met up with a fan and friend Scott Derrickson at a bar in Las Vegas where he pitched his idea for Sinister. Derrickson, showing great interest in this concept, contacted producer Jason Blum who particularly liked the simplicity of the concept and understood the urge to make it as fast as possible before it could be made by anyone else. Shooting of the movie started in September 2011, 6 months after and was first screened at South by Southwest. In an interview with Film.com, Cargill stated that his days as a film critic were over for the time being due to his success and dedication to his new-found career path. "I may pop in every once in a while and write up reviews, but ever since I was a child, I've wanted to be a fiction writer, and now I have the chance to do it in both formats that I am in love with." Sinister was released to positive reviews with many praising the snuff film segments, directing, cinematography, atmosphere, and acting. It was a box office success grossing over $87 million on a $3 million budget. Both Cargill and Derrickson returned as writers for Sinister 2 (2015), which was directed by Ciaran Foy. Unlike its predecessor, the sequel was critically panned. Many criticisms were aimed at the overuse of jump scares, horror cliches, story, and heavy amounts of excessive violence and gore. Cargill and Derrickson were working on a movie adaptation of the Deus Ex video games. They both left the project after Kevin Feige hired them to work on a film adaptation of Doctor Strange in 2014, which would become the 14th film in the Marvel Cinematic Universe. Cargill, along with Derrickson and Jon Spaihts, worked on the script for Marvel's Doctor Strange (2016). The film received positive reviews from critics and audiences, With praise being aimed towards the acting, special effects, and musical score. It grossed over $677 million worldwide. Cargill and Derrickson were set to return for Doctor Strange in the Multiverse of Madness but left due to "creative differences". Sam Raimi was hired to helm the project after they left. More recently, the writing duo of Derrickson and Cargill signed a deal with Blumhouse Television. Cargill, under the pseudonym of Kit Lesser, wrote a biopic about FBI agent William Hagmaier (played by Elijah Wood) and his relationship with serial killer Ted Bundy. "There have been a lot of movies and a lot of media made about Ted Bundy, and one of the things that bugged me a lot was that it's all kind of selling the myth of Ted Bundy and kind of glorifying him in a way," Cargill told Jordan Gass-Poore, the host of the horror-comedy podcast, Pod of Madness. "And the deeper you dig into the story you realize there's nothing to mystify here, there's nothing amazing about him." The film was released in 2021 as No Man of God. Derrickson's departure from directing Doctor Strange in the Multiverse of Madness led him to The Black Phone, a project he and Cargill had already planned on making. It is an adaptation of Joe Hill's short story of the same name. The film premiered at Fantastic Fest on September 25, 2021, and was theatrically released by Universal Pictures on June 24, 2022. It has grossed $157.2 million and received generally positive reviews from critics for its performances and faithfulness to the source material. It received praise from Joe Hill. In October 2023, the sequel was officially announced by Universal Pictures with a scheduled release date of June 27, 2025. The following month, it was reported that Hawke, Thames, McGraw, Davies and Mora would reprise their roles in the sequel. Derrickson and Cargill also returned to write the script. Cargill and Derrickson will also team up to write the script for The Outer Limits, a movie based on the influential 1960s television show of the same name. The film, produced by MGM, will be adapted from a single episode of the classic show, "Demon with a Glass Hand."

Cargill wrote his first article in 2000, when he volunteered to write a review of the movie Crouching Tiger, Hidden Dragon for a website called "Guerilla Films." His article managed to get the highest amount of traffic of over 50,000 hits, "a HUGE deal" at the time, which secured him the job to write more reviews. While working for Guerilla Films, Cargill began spending time with Ain't It Cool News' Eric Vespe (AKA 'Quint' on the site), which landed him a job on Ain't It Cool's "Indie Indie Column," a previously abandoned post. He began writing for Ain't It Cool News under the name Massawyrm in May 2001. His first review for the blog was of Jon Favreau's movie, Made. During his work as a blogging critic, Cargill met various directors, which occasionally led to small roles in independent productions. In 2011, he told Jordan Gass-Pooré with Slackerwood that it was getting "tougher and tougher" to write movie reviews because of his relationships with people in the movie industry. "I've always had a strict code about writing about films made by people I'm friends with," said Cargill. "It's harder to write objectively about film without people feeling that you're being biased." Besides his work for Ain't It Cool News and his involvement with Spill.com, he also did freelance work for Film.com and Hollywood.com (the site that owned Spill.com).