Caroline Lucas, Brighton Pavilion MP was arrested outside energy company Cuadrilla's exploratory oil drilling site in Balcombe, West Sussex, last August 19.
She 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."
Ms Lucas's co-defendants - Josef Dobraszczyk, 22, from Bristol; Ruth Jarman, 50, from Hook, Hampshire; Sheila Menon, 42, from London; and Ruth Potts, 39, from Totnes, Devon - were also cleared of both charges.
Ms 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.
Ms Lucas told the trial that governments were failing to 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.
The cost of policing the protests at Balcombe was nearly £4 million, prompting Sussex police and crime commissioner Katy Bourne to seek financial aid from the Home Office.