He began his career writing and directing the 1999 short film 9 Across, starring Rena Owen.
[citation needed] He then segued to television work, directing for series such as, Legend of the Seeker, V, Criminal Minds, The Vampire Diaries, The Originals and True Blood.
[citation needed] In winter 2014, Warn directed his first episode of the DC Comics produced Green Arrow origin series Arrow, which was episode 19, of season 2, "The Man Under the Hood", and featured characters crossing over from the series' impending spin-off, The Flash.
Warn directed the third episode of The Flash's first season, "Things You Can't Outrun", which featured the introduction of future-superhero Ronnie Raymond.
[citation needed] He directed the 8th episode of Arrow's 3rd season, "The Brave and the Bold", which again featured a crossover event with The Flash.