The actor is seen for the first time as Assange in forthcoming movie The Fifth Estate which has now begun filming.
It traces the early days of his WikiLeaks site as he sought to bring confidential information into the public domain.
Cumberbatch - famed for his role as Sherlock Holmes in the BBC One update of Conan Doyle's stories about the consulting detective - stars alongside Daniel Bruhl, who portrays Daniel Domscheit-Berg, one of his early supporters.
The film is based on two books about the rise to infamy of Assange, who is holed up in Ecuador's London embassy after being given asylum. The Australian faces extradition to Sweden over sexual assault claims, which he denies.
Director Bill Condon said: "It may be decades before we understand the full impact of WikiLeaks and how it's revolutionised the spread of information.
"So this film won't claim any long view authority on its subject, or attempt any final judgment. We want to explore the complexities and challenges of transparency in the information age and, we hope, enliven and enrich the conversations WikiLeaks has already provoked."
Assange himself has hit out at the film as a "massive propaganda attack" against the whistle-blowing website.
Delivering a speech to the Oxford Union from the embassy, he revealed he had acquired a script and said the film, being released in the US in November, was also an attack on Iran.
Reading from the script, he said the opening scene was inside a military complex in Iran, with documents containing nuclear symbols. The suggestion is that Iran is working on an atomic weapon, said Assange, adding: "How does this have anything to do with us? It is a lie upon lie. The movie is a massive propaganda attack on WikiLeaks and the character of my staff."