A judge at Westminster Magistrates’ Court acquitted her of a single charge under the Public Order Act on Friday.
She and four others, aged between 19 and 59, were accused of failing to comply with an order by police to move their protest to a designated area near the conference.
At the hearing at Westminster Magistrates’ Court, she was joined by two Fossil Free London (FFL) protesters and two Greenpeace activists who also pleaded not guilty to breaching Section 14 of the Public Order Act 1986.
But Judge John Law ruled that the condition placed on the protest was unlawful because police could have imposed lesser restrictions and because the conditions were not clear.
The judge said the protest was “throughout peaceful, civilised and non-violent” and criticised evidence provided by the prosecution about the location of where the demonstrators should be moved to – saying the only helpful footage he received was “made by an abseiling protester”.
He added: “It is quite striking to me that there were no witness statements taken from anyone in the hotel, approximately 1,000 people, or from anyone trying to get in.
“There was no evidence of any vehicles being impeded, no evidence of any interference with emergency services, or any risk to life.”
Footage was played to the court in which Miss Thunberg said “I’m staying” when asked to move by police constable David Lawrence.
The climate campaigner could be seen laughing while footage of her being escorted away was played.
The court heard that protesters started to gather near the hotel in October last year at around 7.30am and police engaged with them about improving access for members of the public, which the prosecution alleged had been made “impossible”.
The judge rejected the submission as “the main entrance was accessible (meaning) that the condition… was unnecessary when the defendants were arrested”.
The Swedish national blocked Hamilton Place, near Park Lane, on the first day of the Energy Intelligence Forum, where a number of senior CEOs, businessmen and political figures had gathered to discuss sustainable solutions to world energy challenges.
At around 7.15am, a number of activists gathered at the location and began to block the hotel entrances and security exits. By 10.23am, protesters had gained access to the roof of the building and were slowly abseiling down, while a vehicle entrance was also blocked by midday.
Superintendent Matt Cox, who was in charge of policing on the day, told the court on Thursday: “Essentially the delegates weren’t able to get in and out of the hotel. It was relayed from security that people weren’t able to get out of the hotel. People were really restricted on how they could access the hotel.”
Those affected included a group of 30 guests who were due to catch flights. The court heard that after repeated engagement with the activists, police imposed a Section 14 order and began informing protesters that they were required to move to a designated protest area on the pavement.
Outside the court on Thursday, Ms Thunberg made a statement in which she said: “Even though we are the ones standing here, climate, environmental and human rights activists all around the world are being prosecuted, sometimes convicted and being given penalties for acting in line with science.
“We must remember who the real enemy is. What are we defending? Who are our laws meant to protect?”
The Metropolitan Police had imposed conditions on the 17 October protest under Section 14 of the Public Order Act to “prevent serious disruption to the community, hotel and guests”.
A further 21 people who took part in the same demonstration, including supporters of Extinction Rebellion, are also due to appear at later court dates.