However drivers are still being warned to avoid the area around Junction 10 in Walsall where the motorway is shut in both directions for the bridge to be installed.
The junction has been shut since Friday evening, with drivers facing 45-minute delays at busy times as they are diverted up and over the junction to keep the carriageway clear for the workforce.
The last two pairs of beams, which are all 44 metres long, were lowered into place at 6.30am on Sunday. Highways England said the scheme was going ahead of schedule but the motorway would still remain closed until Monday morning.
The huge crane used to install the beams was dismantled on Sunday morning ahead of being transported back to the West Country in the afternoon.
Drivers heading in the same direction were warned to expect a slow-moving six-vehicle convoy heading south on the M5.
It is the second time in two months that Junction 10 has been shut as part of a £78 million scheme to reduce congestion through the Black Country.
In August beams were installed for the north bridge over the junction, with this weekend's work focusing on the south bridge.
Motorists heading north were encouraged to use the M1 instead of the M6 and allow lots of extra time.
Among the drivers facing long journeys on Sunday were Wolves fans heading south to watch their side play Southampton.
Ahead of the closure, National Highways project manager, Annie Hyett, said: “We only shut motorways if absolutely necessary and appreciate the impact closures have on people.
"For the safety of all involved, we have to close the road this weekend while these heavy beams are lifted into place across the motorway using very large, specialist crane and plant equipment.
“We know there are likely to be significant delays at times and would remind anyone travelling along the M6 this weekend or in the local area to take alternative routes if at all possible.
“Once the new bridges are installed and the junction improvements completed drivers will be able to enjoy much smoother, safer and more reliable journeys.”
Further closures will be in place throughout the autumn, with Junction 10 due to be shut from 8pm to 6am every weeknight from Monday until October 20 while bridge deck panels are installed.
On Saturday, October 9, the stretch of motorway will close at 8pm until 6am on Monday October, 11 so more of the panels can be lifted into place.
The same up and over diversion will be in place for every closure.