Derby City Council has approved £34m plans to redevelop its headquarters.
The interior of the Council House on Corporation Street will be stripped out, creating open-plan spaces with a new council chamber at the centre.
The authority said the current building needed modernising and has a £14m maintenance backlog.
It claims the revamp will allow the headquarters to accommodate more employees, who will be moved from other "inefficient" office buildings.
Under the proposals, the St Mary's Gate and Roman House sites will be sold in 2013/14 to generate about £4.6m, while the rent paid for other council buildings will be reduced.
An extra storey will also be added to the new building, which the council plans to "rent out to partner organisations".
Six of the nine members of the planning committee voted in favour of the plans on Thursday evening, with the remaining three abstaining.