Historic Scotland and Highland Council have granted scheduled monument consent and planning consent for the £2.36 million restoration of Mingary Castle, a 13th century ruin on the Ardnamurchan Peninsula.
Emergency work is already underway. The plan is to provide holiday accommodation as well as to take on a community role.
"The approval of extensive repair works to the Castle will ensure that this historic structure will survive for future generations," said Francis Shaw of Shaw and Jagger Architects, which has drawn up the plans for the Mingary Castle Preservation and Restoration Trust.
It stands by the sea, a mile or so to the east of the village of Kilchoan.
It was the seat of the Clan MacIain, a branch of Clan MacDonald and once one of the most powerful clans along the western coast of Scotland.
According to the trust some believe it was the MacDougalls who were responsible for the original construction but it is equally possible that it was a MacDonald castle from the start.
However it is clear that Mingary did become one of a chain of castles in the MacDonald Lordship of the Isles.
The name Mingary, or Mingarry, may be the Anglicised version of Mioghairidh, but the exact meaning of the word is cause for dispute. A possible translation is that it is derived from two Norse words, mikil, meaning great, and gardhr, a garth or house, so "great house" - though the name has been translated by some to mean "great land between machair and moor".
The Norse derivation suggests that the site was occupied in Viking times.
The castle is the property Donald Houston, 53, who set up the preservation trust to raise money and oversee the work. He has said all the records relating to the castle will available
William Kelly of Mingary Castle Preservation Trust said Historic Scotland had been instrumental in ensuring the schemes' proposals were a success and could be supported by the Highland Council by approving sections of emergency works while the details of the restoration were developed.
The trust is trying to raise funds in support of the restoration works and to maintain the historic building.
The mortar, analysed by The Scottish Lime Centre, was found to be what is commonly known as "Roman Concrete"; how this technology ended up on the edge of ancient Scotland and not used by the English contemporaries is a mystery and is being researched as part of the analysis of the Castle's history.