An Environment Agency severe flood warning - meaning danger to life - was removed from the A361 between East Lyng and Burrowbridge on 10 March.
Residents in the area saw their homes cut off and experienced long diversions as a result of the closure.
The road has been inspected by council highways officers and reopened at 17:00 GMT.
There is still some water on a short stretch of the road and Somerset County Council said temporary traffic lights will be installed to protect the carriageway and allow motorists to pass safely.
Councillor Harvey Siggs, responsible for Highways, said: "I'm delighted the A361 is to reopen at long last.
"Our highways teams have been working hard all week to clear the road and make sure it is safe, and I would like to publicly thank them for their efforts to get this key route open before the weekend."
A further inspection will take place early next week and the temporary traffic lights will be removed as soon as the remaining water has receded and the road judged to be safe, the council said.
Mr Siggs added: "Although the road is clear, the rhynes at the side of the road remain full of water so I would urge motorists to take extra care when driving, particularly in the foggy conditions we have seen over the last few days."
The clear-up of the A361 started on Monday with the removal of fallen trees and the cutting back of damaged vegetation.
Around 30 tonnes of used sandbags were removed before a sweeping and cleaning operation covered the 1.5 mile section of carriageway.
The council said that the road closure on the A372 Langport Road will remain in place next week for the removal of flood pumps.
With improving weather conditions the large temporary pumps at Beer Wall, near Aller, are no longer needed, it added.
The Environment Agency expects to begin removing the pumps on Monday and work is likely to take up to four days.
The road will remain closed after the pumps have been removed so the council can assess flood damage and carry out emergency repair works.
A road on the Somerset Levels which closed in December when it was engulfed by flood water has finally reopened.