Bolton Council staff are to move into Knowsley House in Knowsley Street.
About 120 Finance Department workers will transfer from the Town Hall on July 29. A spokesperson said the space vacated would be used for other council business.
Property specialist Jeremy Rubin & Co has let 10,600 sq ft of refurbished open-plan office space on behalf of Gordon Moon Properties.
The rental deal is worth more than £100,000 a year.
Mr Nigel Moon of Gordon Moon Properties said: "We are very pleased that Bolton Council is keen to take this quality refurbishment that we have undertaken and it shows our confidence in making a large investment in Bolton town centre."
Mr Jeremy Rubin, managing director at Jeremy Rubin & Co, said: "It has been a while since a deal of this size has taken place in Bolton and we are proud to be part of it."
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