Highland Council - which owns the threatre and had previously given £2.35 million towards the scheme - is now granting an extra £600,000.
Costs on the project, which was originally scheduled to reopen last Christmas, have escalated by £3 million to nearly £23 million.
According to theatre bosses, additional repairs to the 30-year-old theatre and the nearby 19th-century Bishop's Palace will run to an extra £2 million while an extra £1 million is needed for 'unforeseen issues'.
Highland Council's chief executive Arthur McCourt hailed the authority's move as the 'last brick in the wall' for Eden Court.
The news follows the Scottish Executive's decision to donate £1.5 million towards the rescue package needed to complete the extension and refurbishment scheme.
This includes constructing a second theatre, two cinemas and extra studios. The historic Bishop's Palace will be renovated to provide meeting rooms and offices while a new dressing-room block will be built along with improvements to public areas.
Highland Council and the Scottish Executive are just two of five sources plugging Eden's funding hole.
Highlands and Islands Enterprise is contributing £600,000. A further £200,000 has been awarded by Eden Court fundraising, while the European Regional Development Fund is giving £100,000.