That meets a pledge by the Waitaki District Council that adding the project cost to rates bills would only be a last resort to pay for the $9.7 million restoration and redevelopment of the 101-year-old building and an extra "wish list" of fittings.
Yesterday, Minister of Internal Affairs Rick Barker presented Waitaki Mayor Alex Familton with a large cheque - in size and amount - for $3,735,608.
The final amount of the grant, from the Lottery Grants Board's significant projects fund, will depend on a final audit of the project and extra fittings the council had originally cut from the project but hoped to complete.
The fund has $16 million to distribute this year and the Opera House grant represents almost a quarter of that.
"This is a huge day for us - a totally historic and significant occasion," Mr Familton said.
The lottery fund makes money available for development projects that benefit the wider community.
It is for projects that have received funding from other sources, but are still unable to raise sufficient money to complete the job.
Mr Barker said the Opera House project would make a major contribution to Oamaru and the whole of the Waitaki district.
"This is a biggie," he said about the grant.
"I think Oamaru may not believe its luck."
The council had made $3 million available from its property fund - mainly from its Forrester Heights residential subdivision on Cape Wanbrow.
The Community Trust of Otago contributed $1.5 million, another $1 million had come from the lottery board and the Oamaru Licensing Trust gave $400,000.
Other money had come from community fund-raising events, donations and grants.
The council's Opera House project manager, Stephen Halliwell, said the lottery board grant meant there would be no debt against the project and no direct input from ratepayers.
Mr Familton said yesterday was a "historical milestone of national importance".
"It is a further step in the preservation and promotion of our heritage - which is second to none."
Jacqui Dean, instigator of the restoration project, said she was always confident funding could be raised.
The former Waitaki deputy mayor and now the MP for Otago knew the redevelopment was going to be a big project, but drew a comparison with the Waitaki Aquatic Centre, which opened in 2000.
"I'm really pleased for the Opera House and the people who have taken up the project doing the hard, hard slog to raise the money," Mrs Dean said.
Former Waitaki mayor Alan McLay was another who embraced the project, one of the factors that led to his defeat at last October's local-body elections.
He felt vindicated that about $10 million had been raised without the need to add to rates bills.
"I always thought we could do it, but only with the wide co-operation of the community."
