Julian Assange pads out from the room in the Ecuadorian Embassy he’s called home for the past year, greeting me with a polite kiss on both cheeks. He’s dressed in an old T-shirt, worn-in jeans – and he’s wearing white towelling socks without shoes.

Well, it is the hottest day of the year, and this is his home. I crack an obviously hilarious joke about dressing up for the occasion as we wander into another room for our exclusive interview about the WikiLeaks’ founder’s bid to run for a seat in the Australian Senate.

The embassy is in Knightsbridge, minutes from Harrods, but once inside – past the smiling Met officer, through the security detector, surrendering my passport – it’s fairly underwhelming. I wait in the small reception area, corridors leading off to various rooms, and busy people chatting in Spanish.

It’s humid, no air-con – and it’s even hotter in the room we go into to talk, with computers dotted around it, a green screen for filming, and Post-it notes on one of the walls with soundbites written on them, such as ‘Cablegate’.

Assange, 42, grew up in Australia. As a teen he hacked into government computers, got raided by the Feds, and started an underground magazine. By 2010 he’d hit headlines as editor-in-chief at WikiLeaks, publishing secret information from anonymous sources.

Using high-profile media, that year the organisation released hundreds of thousands of US military cables, painting a devastating picture of the wars in Iraq and Afghanistan – damning evidence about civilian casualties and ignored torture.

The US and UK condemned the leak. Soldier Bradley Manning was arrested on suspicion of passing classified documents to WikiLeaks, and is now on trial in the US. Assange has described it as a “show trial”, with WikiLeaks helping to fund his defence – as well as supporting the latest whistleblower to go public, Edward Snowden.

Later in 2010, Assange was accused of sexual offences by two women in Sweden. Although he admits he had consensual sex with them, the activist denies wrongdoing, dismissing it as a ruse for the US to extradite him to possibly stand trial over the leaking of military cables. After a legal battle against extradition to Sweden, in June 2012, Assange was granted political asylum at the Ecuadorian Embassy.

Assange is one of the world’s most controversial figures, with two films being released this year – documentary We Steal Secrets (which WikiLeaks dismissed as lies) and thriller The Fifth Estate, starring Benedict Cumberbatch as the WikiLeaks founder. This week, Assange will be officially announced as the WikiLeaks Party candidate for an Australian Senate seat in Victoria.

The other candidates for New South Wales, Western Australia and Assange’s running mate in Victoria will be announced on Thursday. However, one of the pressing issues is that Assange isn’t in Australia – he’s sitting in a chair opposite me, his silver-blond hair long and unkempt, and even lighter than it appears on TV or in photos.

He speaks in a low, gravelly tone – though the Australian accent is there. Pausing on a few occasions to find the right word, making sure he doesn’t say the wrong thing, Assange seems incredibly guarded, placing his dictaphone next to mine to record the interview, saying he’s been burnt many times by the media. Every now and then he relaxes, breaking into a laugh or a smile.

He warns me of his tendency to give long answers – and more than five minutes in, I’ve only asked the first question. Our 15-minute allotted slot soon creeps to 45. Here’s the outcome of when TNT met Assange.