John Brown, an officer with Strathclyde Police, was accused of striking Sean Black over the head with a bottle and stamping and kicking him following the night out in Clarkston Hall, Glasgow, in August 2011.
The charge against Mr Brown, of East Kilbride, alleged he "acted with others unknown" and assaulted Mr Black "to his severe injury and permanent disfigurement".
Mr Black claimed the 24-year-old attacked him after a fight broke out between his group of friends and the officer's, but jurors at Paisley Sheriff Court returned a unanimous not guilty verdict after more than two weeks of evidence.
Mr Brown's solicitor, Michael Vaughan, of law firm Levy & McRae, said his client was "extremely relieved" to be cleared.
The police officer appeared in court with three other men – Peter Campbell, 51, of Rutherglen, and David Graham, 27, and Sean O'Hara, 21, both of Cambuslang.
Campbell and Graham were convicted of assaulting Mr Brown's friend James Paterson by punching and kicking him and striking him over the head with a bottle, while Mr O'Hara was cleared of the same offence.
Campbell was also found guilty of another assault.
The court heard that the incident began at around 11.30pm as the men waited for taxis. Mr Brown admitted he was present and told the court he saw Mr Paterson being attacked but denied attacking Mr Black.