The victim, a 33-year-old local man, lost a tooth and sustained a large gash to his lip and a black eye, when he was assaulted by another man at Rehab Bar on Parliament Street at around 2.45am on Friday 20 June 2014.
The injury to his lip will leave a permanent scar.
A 35-year-old local man has been arrested in connection with the incident and has been released on police bail as enquiries continue.
Officers believe that there were a lot of people in the bar at the time of the incident and are urging anyone who saw what happened to come forward.
A spokesperson for Rehab said: Although a rare occurrence, this is a very serious and disappointing incident to happen in our venue and we would urge people to support the police in their enquiries and and to provide any information they have.
Anyone who can help officers with their enquiries is urged to contact North Yorkshire Police on 101 – select option 2 – and ask for Detective Constable Fiona Saunderson or Harrogate CID.
Alternatively, information can be emailed to email@example.com
If you prefer not to give your name, Crimestoppers can be contacted anonymously on 0800 555 111.
Please quote reference number 12140100181 when passing information about this incident.