The 36m-high, 125m-long viaduct, near Tuatapere, has been restored.
The structure was initially built in 1925 to help transport logs to the Port Craig mill. It has since been used by walkers on the Hump Ridge Track.
According to the Port Craig Viaducts Charitable Trust, the Percy Burn Viaduct is regarded the world's largest wooden mill tramway.
In 2013 the viaduct was closed by the Department of Conservation and a bypass put in place because of safety concerns about the decay and corrosion of key structural elements.
Doc, Southland District Council, and the Port Craig Viaducts Trust partnered to ensure the wooden structure could be reopened.
The total restoration cost was $710,000. Doc put up $380,000, while the council and viaducts trust raised the rest.
Port Craig Viaducts Trust chairman Tom Pryde said given the various challenges the restoration was a major feat.
"This is a significant project when we consider the age of the structures and the magnitude of the restoration work, as well as the remoteness of the work sites in southern Fiordland."