This means the ancient capital will no longer have any banks or counter services, with Lloyds Bank branch previously shutting in 2020.
Its currently only serving three days, with the official closing date to be on February 9 2024.
The bank has announced that it has successfully received planning permission for a new ATM machine to be installed at the Castletown Commissioners building which will be available to use from before the closure date.
A statement to customers added: 'We realise this might not be welcome news and we are sorry for any inconvenience it may cause.
'However, we would also like to take this opportunity to reassure you that we’re still here for you in our branches in Douglas and Ramsey and continue to be ready to support you face-to-face in Castletown, up to the date we close.
'We’ll be closing our Castletown branch on 9th February 2024 but we’ll make sure you and your local community continue to have access to our banking services when you need them, whether at another one of our branches in the Isle of Man, or in a different way via our digital services.'
'Until we leave Castletown, we have placed additional support in the branch who can help you. We look forward to continuing our relationship with you from our other branches in the Isle of Man and would like to take this opportunity to thank you for banking with us.
'We’ll be working with the local community to understand the impact of closing this branch. Once we’ve gathered feedback, we’ll publish the results in a booklet called ‘Branch closure feedback’, which you can get from your branch or online, in the meantime you will find a reasons for closure booklet on our site. 'If you have any questions or would like to discuss anything related to your account(s), please don’t hesitate to get in touch with your usual Barclays contact or call the Service Centre on +44 (0) 1624 684 444** and a member of the team will be happy to help.'