Theresa Norton, 65, and Mair Bain, 36, were found to have breached the injunction when they protested on the M25 with 10 others in November 2022.
Delivering his ruling at the High Court in London on Monday, Mr Justice Soole said both defendants had crossed the custody threshold.
He decided not to impose any penalty against the remaining 10 defendants also found in contempt, including 76-year-old grandmother, Gaie Delap, who climbed on to an M25 gantry.
Her actions caused massive disruption to the M25 and members of the public
Mr Justice Soole
The retired teacher from Bristol previously told the judge that her “heart was breaking” for the future of her six grandchildren.
Mr Justice Soole found that she and nine of the others had not been made aware of the injunction by a Just Stop Oil mentor prior to the protest, describing the omission as a “significant failure and breach of trust”.
He handed Bain a 40-day jail sentence suspended for two years and Norton an 80-day sentence, also suspended for two years, telling the court: “Her (Bain) actions were deliberate and in defiance of the court.
“Her actions caused massive disruption to the M25 and members of the public.
“The mitigating factors include her apology and her statement explaining she would not breach court injunctions in the future.”
He described Norton’s case as “much more difficult” due to her previous conviction for being in contempt of an injunction and past comments by her explaining that she would continue to “protest regardless and defy the court”.
Mr Justice Soole took into account her statement which explained she had “no intention” of breaching court orders in the future.
Referring to the 10 defendants who had no knowledge of the injunction, he said: “It would have been a significant failure and breach of trust for JSO not to have told the volunteers of the potential consequences (of breaching the order).
“Having listened to each of these defendants my conclusion is that each of them have told the honest truth.
“I do not accept that they have lied to the court.
“It is surprising that the so-called legal brief did not give reference to existing injunctions but in my judgment it is not incredible.”
Outside court a spokesman for Just Stop Oil said: “Today no-one was imprisoned or fined, but the fact that 12 people have spent over a week in court, facing the loss of their freedom for disobeying a ‘private law’, and now face criminal charges for the same action, demonstrates our courts are not protecting the ordinary people of this country, but defending those making profit by killing people.”
A spokesman for National Highways, which brought the case against the protesters, said: “Our primary concern is always safety – protesting on the strategic road network is extremely dangerous to the protesters and motorists.
“It’s right that dangerous and reckless protesters who disrupt our strategic road network should face the necessary consequences; anyone intending to protest on these roads protected by an injunction should know that they run the risk of imprisonment and an unlimited fine.
“People rely on the strategic road network for so many things and they have a right to expect it to operate as it should.”