Vehicles were allowed on to the eastbound carriageway of the new M8 for the first time on Sunday, a week after the westbound carriageway opened.
It means the entire stretch between Edinburgh and Glasgow is now motorway.
The works were the latest stage in the Â£500m M8, M73 and M74 motorway improvements project.
The completion of the missing link means drivers no longer need to use the old A8 between Newhouse and Baillieston.
Transport Scotland said the new road layout was expected to cut journey times at peak periods by up to 20 minutes.
However, temporary speed limits will remain in force at various locations to allow remaining works to be completed safely.
Graeme Reid, project manager with Transport Scotland, said: "This is a huge milestone in the project.
"It has been ongoing for three years and this is a huge section of brand new motorway open in both directions between Edinburgh and Glasgow for the first time.
"Drivers have been patient during that time and we thank them for that. The end is very much in sight and drivers will experience the benefits during the week."
Transport Scotland said 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.
Drivers were urged to plan their journeys in advance using the Transport Scotland and Traffic Scotland websites.
Scotland's busiest motorway has opened fully to traffic following the completion of the so-called "missing link".