Speaking to Oxford University students via a video linked from his asylum at London's Ecuadorian embassy, Assange dubbed the movie a "massive propaganda attack" and questioned the accuracy of West Wing writer Josh Singer's script.
Assange referenced specific scenes from the script, notably an early sequence inside an Iranian military compound that clearly displays nuclear symbols, reports The Guardian.
"How does this have anything to do with us? It is a lie upon lie," he said. "The movie is a massive propaganda attack on WikiLeaks and the character of my staff."
Assange added that The Fifth Estate was "fanning the flames" of war and contained "a lie" about meetings between US agents and scientists.
The Fifth Estate, directed by Twilight: Breaking Dawn helmer Bill Condon, released its first picture earlier this week.
The still shows a blonde-haired Cumberbatch as Assange standing alongside business associate Daniel Domscheit-Berg (Daniel Brühl).
Laura Linney, Anthony Mackie, David Thewlis, Peter Capaldi, Alicia Vikander and Carice van Houten feature in the supporting cast of the drama.
The Fifth Estate is due in US cinemas on November 15, while a UK release date has yet to be announced.