Holyhead's Market Hall was built in 1855 but has fallen into a state of disrepair in recent years.
Anglesey council took over its ownership through a Compulsory Purchase Order last year and secured a Â£2.4m Heritage Lottery grant to restore the Grade II Listed building.
Restoration gets underway in the next few weeks, starting with the roof.
The whole  project will be done in two stages, with the end of 2018 earmarked for completion.
On Friday local businesses were given a guided tour inside the building and shown the plans, which include a new library and market hall.
Anglesey council assistant chief executive, Annwen Morgan said: "Such remarkable historic buildings are irreplaceable.
"If no one intervenes then these rare buildings not only disappear forever from our townscapes, but so do the stories that they tell us about the lives of our recent ancestors."
Work is set to begin on restoring a historical Anglesey building to its former glory.