Caroline Lucas has vowed to continue her fight to end fracking after being found not guilty of obstructing a public highway and a public order offence during high-profile protests.
Britain's only Green MP was arrested outside energy company Cuadrilla's exploratory oil drilling site in Balcombe last August 19.
The Brighton Pavilion MP was among a group of protesters who had linked arms outside the site, which had become a national focal point for anti-fracking protests.
During the trial at Brighton Magistrates' Court alongside four co-defendants, Lucas, 53, said she "wanted to express solidarity" by protesting peacefully.
She was found not guilty of the two charges she faced - wilful obstruction of a public highway and breaching an order under Section 14 of the Public Order Act.
Outside court, she said: "We are pleased that the court upheld our right to peacefully protest against fracking, but this judgment is not a victory or cause for celebration.
"We will continue to campaign to end fracking and only celebrate when our world is on the path to a clean energy future."
Dr Lucas's co-defendants - Josef Dobraszczyk, 22, from Bristol; Ruth Jarman, 50, from Hook, Hampshire; Sheila Menon, 42, from north east London; and Ruth Potts, 39, from Totnes, Devon - were also cleared of both charges.
Dr Lucas told the trial she felt it was important to protest about fracking in a bid to prevent the UK being locked into using more fossil fuels.
She said: "I'm haunted by the idea that my children and my children's children will turn round to me and say, 'What did you do about this overwhelming threat?'
"And I want to do all I can do peacefully to address that before it's too late.''
Thanks so much for all messages of support - This is victory for whole movement against dirty fracking & for cleaner energy #frackingontrial— Caroline Lucas (@CarolineLucas) April 17, 2014
Dr Lucas told the trial that governments were failing to urgently address the issues surrounding climate change.
And she said she felt the protest outside Cuadrilla's main entrance was a "legitimate'' and "appropriate" way of sending a message to the Government about fracking concerns.
Last summer's anti-fracking protests at Balcombe placed the controversial extraction method under forensic scrutiny.
Although Cuadrilla did not frack at the site, its drilling operation sparked concerns that it would go on to do so in the future.
Prosecutor Jonathan Edwards told the trial that a large camp formed near the site's entrance and extra officers were drafted in because of the vast number of protesters.
A notice under Section 14 of the Public Order Act was imposed, requiring demonstrators to use a designated protest area away from Cuadrilla's entrance.
Dr Lucas told the trial it felt important and "symbolic" to be based outside the main gate during the protest, which lasted about five hours from around 10.15am.
Giving evidence, she denied being told of a designated protest area by police, adding: "I couldn't see any reason why we couldn't continue our peaceful protest."
Pc Robert Staplehurst, of Sussex Police, told the court he approached Ms Lucas, said there was a Section 14 notice and asked whether there was anything he could say to move her.
Dr Lucas - who was elected as the Green Party's first MP in the 2010 general election - replied no and was arrested.
She went on: "If we had another 10 to 15 minutes we could have come to an agreement to end it and dispersed. We weren't doing anything different than we were in the previous five hours."
A short section of footage was shown to the court showing Ms Lucas circled while linking hands with fellow protesters.
In it, Pc Staplehurst is heard to say: "I require you to move. Are you going to move of your own accord?"
He went on: "Just bear in mind you will be arrested...is there anything that I can say that is going to make you move? In that case, Caroline, I'm arresting you."
In another section of footage, Ms Lucas and fellow protesters are seen singing: "We shall not, we shall not be moved."
Under cross-examination, Ms Lucas said she did not believe the protest would have had the same impact if it had taken place away from the main gate.
And she was questioned about whether the singing of "We shall not be moved" was an indication of defiance of the police.
Ms Lucas said: "It was more the fact that we were singing together rather than the words we were singing. It's a song of strength."
Fashion designer Dame Vivienne Westwood sent Ms Lucas a message of support during the trial, and said fracking should be halted until the public was made aware of the "true facts".
Hydraulic fracturing - or fracking - involves high pressure liquid being pumped deep underground to split shale rock and release oil or gas supplies.
Fears have been raised over the potential for small-scale earthquakes and water pollution, and that a drive to exploit new gas reserves will turn the focus away from efforts to develop a low-carbon economy to tackle climate change.
Cuadrilla drilled horizontally for some 1,700ft through Micrite formation, a type of limestone, at a depth of around 2,350ft below ground level.
But later its chief executive Francis Egan said the rock underneath the drill site, at Lower Stumble, was already naturally fractured, and the company had no intention of fracking there.
The cost of policing the lengthy protests at Balcombe was nearly £4 million, prompting Sussex police and crime commissioner Katy Bourne to seek financial aid from the Home Office.