Sheffield Council has registered the Walkley Carnegie Library building as an asset of community value, following an application by users and residents.
The status means the building cannot be knocked down or converted without planning permission. If it goes on sale, the community has six months to put in an offer.
Earlier this year councillors granted True North Brew Co permission to turn the library into a shared venue featuring a café bar. The library section - run by volunteers for almost two years - will be sub-let through the council.
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Library committee chairman Chris Reece said: "It's very good that it has been listed, as that means its services should be retained as a library.
"Under the partnership with True North, the library will continue to operate within a larger-scale building including the café bar."
Walkley is now an 'associate library', which means it is supported by a grant and run independently by volunteers.
The committee will mark two years of being in charge on November 19.
"It's absolutely essential to the community," said Chris. "It's more than just a library. We have a number of events going on, a lot of activities. A lot of people use it to get information from books and the IT system.
"And maybe it's just to keep warm and make friends. There's a definite social base.
"Since it has been run by the volunteers group we are continuing to increase the number of events and activities we put on."
True North has promised to repair the Grade II listed building, create a mezzanine floor inside and add an extension with kitchens, offices, toilets and a cellar.
The company has also promised to raise Â£6,000 per year towards library services. The extension and café bar should open next year.
"The building is in a very poor state," said Chris. "This partnership will take that forward."
Walkley city councillor Neale Gibson said: “It’s really good the council has taken action to protect Walkley Library and it’s yet another example of how we’re working to make Walkley an even better place.”
And cabinet member for community services and libraries Jack Scott said: “Walkley Library is a great community asset which supports lots of different groups as well as the library itself.
"I hope everyone in the local area enjoys using it and want to thank all the volunteers who provide such fantastic services that make such a huge difference to the community.“
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