Emma Thompson is set to narrate a feature doc about Pentagon Papers leaker Daniel Ellsberg, dubbed “the most dangerous man in America” by then U.S. President Richard Nixon.

The Hollywood actress will lend her voice to director Paul Jay’s How to Stop a Nuclear War, which is based on the book Doomsday Machine: Confessions of a Nuclear War Planner by Ellsberg.

In extensive interviews with Jay for the feature, Ellsberg explains the “institutional madness” of American nuclear war plans and how the Russian invasion of Ukraine has made the world far more dangerous, according to a synopsis by the filmmakers.

In a statement obtained by The Hollywood Reporter, Thompson said she had been fearful of nuclear weapons in her youth and participated in protests against their use, and feels a need to get active again.

“Making the connection between the climate crisis movement and the anti-nuclear movement has never been more essential. Between us, we can – to quote Ellsberg – prevent this from happening. We have to start now, today and never stop until these weapons have been outlawed for the murderous evil that they are,” Thompson said.

Ellsberg famously made copies of the Pentagon Papers and classified nuclear documents during the Nixon administration and leaked the documents to the New York Times and other media outlets in 1971. As a high-level Pentagon analyst, Ellsberg was charged by the U.S. with breaking the Espionage Act, but the case was dismissed because of government misconduct in evidence-gathering.

In the upcoming feature doc, still in production, Ellsberg warns that the nuclear weapons arsenals of the U.S. and Russia are still very much a threat to global peace and that an all-out nuclear war remains capable of being launched from missile silos or submarines on a few minutes’ notice.

Jay, a veteran producer and co-founder of the Hot Docs International Documentary Festival, directed Hitman Hart: Wrestling With Shadows. He will helm How to Stop Nuclear War, while Earl Katz (Hacking Democracy) and Rob Johnson (Taxi to the Dark Side) will executive produce.

Toronto-based Jay is also founder, editor-in-chief and host of theAnalysis.news, a news analysis service. He also executive produced the CBC television magazine series CounterSpin and the TV series Show Me Yours.