From 6.30am, protesters again scaled gantries at various locations on the motorway, as they continue to call on the government to halt new oil and gas licences.
Several stretches of the M25 were closed while officers from the Met Police and forces in Kent and Surrey dealt with activists, making at least seven arrests.
Drivers faced delays of up to 70 minutes.
The road had fully reopened by about 9.40am, but National Highways warned motorists to expect residual delays from earlier closures.
Earlier on Thursday morning, Surrey Police arrested two protesters after removing them from two separate sections of the motorway near junctions 7 and 8. The road was shut in both directions from 7.40am, but had reopened by 8.30am.
Near the M25 in Kent meanwhile, officers arrested five people after they stopped a “suspicious car” and found climbing equipment, harnesses, D-locks and banners inside.
Essex Police also arrested a 24-year-old woman attempting to climb a gantry approximately near junction 28 on the M25 clockwise.
Just Stop Oil shared a video taken by an activist perched on a gantry between junctions 8 and 9.
“I’ve only just got up here,” the woman says in the video. “I’ve attached the banner - one on each side. The traffic’s still coming - I’m expecting the police to arrive soon. Here they are. So that was pretty quick.
“I’m here obviously because I feel the need to - why else would I be here? I wish I didn’t have to do this.
“I’m so relieved I’ve put the banners up without causing an accident,” she adds, saying she had been “really worried” about distracting drivers.
Just Stop Oil: M25 Protest
“It’s an immense worry,” she said. “But what else can we do to raise the alarm? We’re in big trouble - we need to stop oil, and that’s why I’m here.”
Animal and climate activism group Animal Rebellion also joined the protests on Thursday.
Just Stop Oil quoted Phoebie Plummer, a 21-year-old student from London, saying: “As a young person, the only future I see before me is one of mass famine, severe droughts, wildfires, floods and societal collapse.
“I understand people must be frustrated with us, and rightly so, but we have to disrupt daily life because we are hurtling towards climate catastrophe.”
Thursday’s Just Stop Oil protest follows similar action on Monday, Tuesday and Wednesday that also brought traffic chaos to the M25.
Wednesday’s protest saw a police officer riding a motorbike injured in a crash involving two lorries, thought to have been caused by a rolling road block. Multiple junctions were closed for hours while protesters were removed from gantries and arrested.
On Wednesday, Home Secretary Suella Braverman made a rare move to criticise officers in the midst of an operation, as she said police forces are failing in their duty to crack down on Just Stop Oil activists disrupting the M25.
Speaking to a chief constables summit in Westminster, she called for a focus on “common sense policing” and told police chiefs she expected “a firmer line to safeguard public order” when it comes to dealing with eco-warriors. “Indeed, that is your duty,” she added.
The Metropolitan Police Events team posted on Twitter on Thursday morning that it was “ready to respond to any criminality on the #M25 again today and will work quickly to minimise disruption and keep traffic moving.”