Delivering a speech to the Oxford Union from the Ecuadorian Embassy in London last night, Mr Assange revealed he had acquired a script of the film, which stars Sherlock actor Benedict Cumberbatch.
Holding a copy of the script, he said the film, being released in the US in November, was also an attack on Iran.
Publicity photographs released earlier shows the actor as Mr Assange in the movie, The Fifth Estate, which has now begun filming.
Attack on Iran
It traces the early days of the WikiLeaks site as he sought to bring confidential information into the public domain.
But Mr Assange said Dreamworks was spending millions of dollars on the film, which he said was “fanning the flames” of war against Iran.
The British public should be concerned about the film because of the involvement of Mr Cumberbatch, said the WikiLeaks founder, who has been inside the embassy since last summer.
He has been granted political asylum by Ecuador as part of his campaign to avoid extradition to Sweden where he faces allegations of sex charges, which he denies.
Reading from the script, he said the opening scene was inside a military complex in Iran, with documents containing nuclear symbols.
‘Lie upon Lie’
The suggestion is that Iran is working on an atomic weapon, said Mr 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.”
The film’s director Bill Condon said on Wednesday: “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.”
Mr Assange spent more than an hour talking to the union, which was celebrating whistleblowers.