Sue Robinson from the pub in West Yorkshire said: "He (Newby) drinks in here all the time so I just asked him if he would be interested in doing it and he was happy to."
Newby is WKF World Karate Champion and a professional boxer who runs martial arts classes.
The aim behind the behind the guest appearance is to raise money for a local hospice Manorlands, which provides palliative care and therapy services to those with life-limiting conditions and support their families.
The pub will be donating 20p to the hospice for every pint the martial arts champion serves and has told Robinson he has a lot of friends turning up for a pint.
Robinson has been at the Robin Hood for the past two and a half years and said: "I think he has been coming here for years, since he was 18, and he comes in three or four times a week."
She has promoted the guest appearance on Facebook and contacted the local newspaper for further coverage.
She added: "This is the first time we have had a guest appearance and I actually read about the idea in the Publican's Morning Advertiser."