Lindsay Mills, thought to have been deserted by Snowden before NSA revelations, appears beside whistleblower in Citizenfour

The mystery of the whereabouts of Edward Snowden’s long-time girlfriend is solved in a documentary that premiered in New York on Friday night: she has been living with the national security whistleblower in Russia since July.

The surprise revelation in the documentary, filmed by Laura Poitras, upends the widespread assumption that Snowden had deserted Lindsay Mills and that she, in a fit of pique, fled Hawaii where they had been living to stay with her parents in mainland US.

Since Snowden, a former NSA contractor, outed himself last year as being behind the biggest leak in US intelligence history, Mills has remained silent, giving no interviews or any hints of her feelings on the subject of her boyfriend or his actions.

The two-hour long documentary, Citizenfour, shows Mills living in Russia with Snowden.

When the Guardian met Snowden in Moscow in July, Snowden suggested the relationship was more complex than the view constantly recycled in the media of a woman abandoned and hinted that the two were not in fact estranged.

Citizenfour offers a fly-on-the wall account of Snowden. Poitras filmed him at the Mira hotel in Hong Kong last year during interviews with journalists that resulted in a series of stories in the Guardian about the extent of surveillance by the US and British intelligence agencies as well as the internet and telecom companies. The revelations started a worldwide debate about the balance between surveillance and privacy.

Poitras captures the tension in his room at the Mira – where then-Guardian columnist Glenn Greenwald and I interviewed him – and in his final minutes at the hotel before he fled after being tipped off that hordes of media were about to arrive. She also filmed at the Guardian in London ahead of publication of one of the most explosive of the stories arising from Snowden’s revelations, and in Moscow, where Snowden is now in exile.

Snowden has been reluctant to talk about his personal life, preferring the media focus to be on wider debate about surveillance rather than him. But Poitras’s portrayal is both personal and sympathetic.

In his first comment about the documentary, which Poitras had shown to him in advance, Snowden told the Guardian: “I hope people won’t see this as a story about heroism. It’s actually a story about what ordinary people can do in extraordinary circumstances.”

Snowden was working as an NSA contractor in Hawaii where Mills joined him. A dancer, she posted many details and photographs about herself and him on the web.

She was still in Hawaii when news broke from Hong Kong that he was the whistleblower. Days earlier, authorities, suspicious about his prolonged absence from work, had visited their home.

On her blog, subtitled, ‘Adventures of a world-travelling, pole-dancing superhero,’ she wrote that she felt “sick, exhausted and carrying the weight of the world”. Shortly afterwards, she took the blog down.

The two appear to have been together since at least 2009, living part of the time near Baltimore before moving to Hawaii in 2012.