The stretch of the motorway at Bowburn near Durham closed on Thursday evening, July 15, following the collision which involved four cars and two lorries, one of which caught fire as a result.
Durham Constabulary confirmed on Friday that two men and one woman had tragically died at the scene.
The A1(M) stayed closed in both directions throughout Friday for investigations into what police said was a harrowing incident.
Large queues formed either side of the closed junctions as traffic was diverted on to nearby roads such as the A167.
Emergency services have confirmed that the road is now clear and reopened in both directions early on Saturday morning.
Formal identification of those who died is expected to take some time.
But the families of those involved have been informed and are being supported by specially-trained officers.
Several other people were also injured with a further two requiring hospital treatment.
A 41-year-old man, the driver of one of the lorries, has been arrested on suspicion of causing death by dangerous driving.
Detective Superintendent Dave Ashton, who is leading the investigation, said: “This was a harrowing incident for everyone involved and our thoughts are with the family and friends of those who have lost their loved ones.”
An online portal has been set up by police to allow people to share information in relation to the incident, including dashcam footage and photographs.
To submit material, please visit https://mipp.police.uk and click on the Durham Constabulary tile. There is an upload limit of 700mb on multimedia files.