The Cube in Corby, which has cost £48m, now has its fourth floor office space completed and available for rent.
The rest of the building includes Corby Borough Council offices, a library, theatre and register office.
Tom Beattie, the council's Labour leader, said: "There was a cost over-run, but we held our hands up and accepted responsibility."
The Cube opened in November 2010, but it had issues, which included a leaking roof.
Building inspectors said the helical staircase was "dangerous, like a helter skelter"  and it was described by the then Conservative opposition leader David Sims as a "poorly managed, waste of taxpayers' money".
Work to bring it up to scratch has now been completed, the council said.
Mr Beattie said: "We know it's taken a while, but we've got a building which is functional, people have got used to it and it makes a statement about Corby's ambition.
"As you see the developments taking place around the town centre, I don't think any of that would have happened without this building being here - it's acted as a magnet to attract further business."
Rob McKellar, current Conservative opposition leader, said: "The Cube is a building Corby can be proud of and it represents Corby's ambitions.
"It was controversial and there are multi-million pound overspends.
"The public did punish the Labour administration at the ballot box in May and Labour has apologised, but now it's time to look to the future and Corby's is certainly a bright one."
Earlier this year, council officer Steven Redfern, reached an out-of-court settlement after launching a £1m damages claim after he turned whistle-blower over the spiralling costs of the project.
Work to finish off a public building, which went £13m over budget, has been completed five years after it opened.