Devlin gradually began writing scripts. His first produced screenplay was for "Universal Soldier". He reached prominence as a writer/producer working alongside director Roland Emmerich, with whom he teamed after appearing in Emmerich's film "Moon 44". Together they cowrote and produced "Stargate," the first movie to have a web site. The team then produced "Independence Day" and "Godzilla". They split following the 2000 Mel Gibson film "The Patriot", but re-teamed to film "" in 2015. Devlin has also produced "Cellular", "Who Killed the Electric Car?", and "Flyboys".