It means the entire stretch between Edinburgh and Glasgow is now motorway.
The work is the latest development in a £500million motorway improvements programme, affecting the M8, M74 and M73.
The completion of the seven mile long ‘missing link’ means drivers no longer need to use a stretch on the A8 between Newhouse and Baillieston.
The new road layout could cut travel time by 20 minutes each way.
Economy Secretary Keith Brown said: “Now the M8 is fully open, commuters between Glasgow and Edinburgh should experience a significant improvement to their journeys between Newhouse and Baillieston Interchange.
“This has significantly reduced the traffic volume on the A8 so that the contractor can focus on completing upgrades to the existing A8 and linking it to the new all-purpose road, which is a continuation of the A8 at Eurocentral.
“Local road users should note that whilst access to all routes to and from the A8 will be maintained, signed diversions for traffic to Coatbridge, Airdrie, Bargeddie and Bellshill will be in place to allow necessary works to be completed.
“I would urge road users to plan their journeys in advance using the Transport Scotland and Traffic Scotland websites.”