Residents of Ovington, near Teesdale, faced a 10-mile detour after the main route to the A67 was cut off by a landslide in December.
The large hole has now been filled and foundations for the bridge and carriageway above have been reinforced ahead of schedule.
Durham County Council said traffic management will be in place while minor works are completed.
Brian Buckley, strategic highways manager at the council, said: "This has been a major project but I am really pleased with how work has progressed and for the patience of the local community.
"We have been able to reopen the bridge to traffic ahead of schedule, which is great."
It was originally thought the repairs would not be completed until mid-September.
