Barclays on High Row in the town centre has been temporarily closed in recent days due to the works.
The nature of the works, inside the listed building are not known.
Customers are being told to use the ‘Barclays Van’ parked nearby to continue banking.
A Barclays spokesperson said: “Barclays’ Darlington branch is temporarily closed while urgent repairs take place.
“To ensure continuity of service, customers can use the Barclays Van located in the branch car park. We will update customers as soon as we have a confirmed reopening timeline.”