“It’s listed because of the extent of its preservation, particularly the formal courtroom, which retains a full suite of its furniture.
“The previous proposal would have seen a bar placed within that courtroom and all of the surviving furniture mentioned in the listing description removed.”
A spokesman for the company said: “We are delighted that we’ve got planning permission for what will be our first pub in the Lake District.
“This is a big step for us, but there is no way we will mess about with what is an important building in Keswick.
“We still have licensing permissions to gain, but if all goes to plan we could see the site open by late this year or early 2015.”
The building was one of dozens put up for sale by Cumbria Police Authority in August 2013 as it attempts to save £20.3m from its budget by 2016.
It had been co-owned by the office of the Police and Crime Commissioner and Cumbria County Council.