Stephen Pritchard and his co-defendants glued themselves to the tarmac, causing huge disruption.
An Insulate Britain protester has been jailed for five weeks for obstructing the motorway, causing huge disruption.
About 10,000 drivers were affected by the actions of Stephen Pritchard, from Bath, and three others on the M4 near Heathrow, west London, in October 2021.
The defendants glued themselves to the tarmac near Junction 3 stopping traffic flow in both directions for two hours.
At Inner London Crown Court, 63-year-old Pritchard was convicted by a jury of causing a nuisance to the public.
His co-defendants, former probation officer Ruth Cook, 71, gardener Roman Paluch-Machnik, 29, and carpenter Oliver Rock, 42, were each given six-week sentences, suspended for 18 months.
The three were also ordered to do 100 hours of community service.
Judge Silas Reid told Pritchard, a former parish councillor, that he was being jailed because he previously told the court that he would not stop taking part in disruptive action, as a matter of “conscience”.
The other defendants previously said they had been deterred from future disruptive protest action.
Judge Reid told Pritchard: “It is not appropriate for me to suspend the inevitable sentence… you will serve up to half of your sentence in prison.”
Speaking to all four defendants, he said: “None of you have shown any remorse for your actions and in fact wear them with pride.”
Last month, Pritchard received a a short jail sentence for defying a court order that prevented him and four others from protesting on the M25.
High Court injunctions were put in place after Insulate Britain’s road blockades last year.