An ambulance had battled through diversions caused by the closure of the Dartford Crossing to reach the crash in Swanley, Kent.
The accident reportedly took place after a woman stopped to help a fellow driver who had become stranded by the side of the motorway.
A vehicle then collided with the women as they waited for assistance on the hard shoulder.
An ambulance, held up by traffic, took 40 minutes to reach the crash scene.
Builder Mark Heap, 55, had also stopped to help the stranded driver and was badly injured in the crash.
Speaking from his hospital bed, he accused protesters of having ‘blood on their hands’.
The nearby Dartford Crossing had been shut after activists climbed onto cables high above the bridge, which links Essex and Kent.
Mr Heap told MailOnline: ‘The eco-warriors may have thought it was an innocent protest, but they’ve got blood on their hands.
‘I don’t think they deliberately caused the crash.
‘But their actions, bringing the traffic to a stand-still on the M20, caused the crash in which those two women died.
‘There was another bad crash on the M2 at about the same time.’
One of Monday’s crash victims has been named as Lisa Webber, a mother-of-four in her 50s.
The other victim, also female, has been described as a GP in her 40s.
The Dartford Crossing protest had ended after Just Stop Oil tweeted they had ‘agreed to cooperate with police’.
The eco-protest saw many drivers rerouted via the M20 in a bid to avoid delays.