Green MP Caroline Lucas and four co-defendants have been cleared of obstructing a public highway during an anti-fracking protest in Balcombe, West Sussex.
Brighton Pavilion MP Ms Lucas and her co-accused were also found not guilty of a public order offence at Brighton Magistrates’ Court.
Ms Lucas was arrested outside energy company Cuadrilla’s exploratory oil drilling site on 19 August last year.
The group had denied the charges.
The other protesters who were cleared are 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.
Giving a statement outside the court, Ms Lucas said: “Protest is the life blood of democracy.
“We are pleased that the court upheld our rights to peacefully protest against fracking but the judgment is not a victory or cause for celebration.”
During the trial, Ms Lucas, Britain’s only Green Party MP and its former leader, defended her decision to take part in the protest and told the court it was important and symbolic to be there.
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.”
She also said she felt the protest was a “legitimate and appropriate” way of sending a message to the government.