In a speech to the Oxford Union from the Ecuadorian Embassy in London on Wednesday, he revealed he had acquired a script of the film, starring British actor Benedict Cumberbatch.
Holding the script, he said the film, being released in the US in November, was also an attack on Iran.
The movie, The Fifth Estate, has now begun filming and publicity photos show the actor as Assange.
It traces the early days of WikiLeaks as he sought to bring confidential files into the public domain.
But 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 Cumberbatch, said Assange, who has been inside the embassy since last summer.
He has been granted political asylum as part of his campaign to avoid extradition to Sweden where he faces allegations of sex charges, which he denies.
The film's director Bill Condon said: "It may be decades before we understand the impact of WikiLeaks and how it revolutionised the spread of information.
"We want to explore the complexities and challenges of transparency in the information age and, we hope, enliven the conversations WikiLeaks has provoked."