The guilty verdict was returned at Sheffield Crown Court just a few moments ago.
Justice Holgate has adjourned sentencing until February 20.
It took jurors just 90 minutes to return a unanimous verdict.
Blue Horrobin, of Highfield Road, Askern was found guilty of killing Lewis Siddall with a deliberate 'haymaker' punch in the VDKA bar in the town centre on August 13, 2015.
The 24-year-old teacher was found dead in his bed the following morning with a fractured skull and fatal brain injury.
Speaking after the verdict Detective Chief Inspector Steve Handley, who led the investigation, said: “Lewis was killed as the result of an unprovoked and senseless act of violence when he was simply out enjoying himself with some friends. This was an avoidable death and shows the devastating effect one punch can have on the lives of the victim, their family and friends.
“This could have been entirely avoided; had Horrobin made a different decision not to lash out with his fists, Lewis would still be alive and well today.
“This was a senseless act that robbed a popular young man of his life, and has robbed a loving family of someone they loved so dearly. No prison sentence will bring Lewis back and they will undoubtedly feel a sense of great loss, sadness and anger for the rest of their lives. I hope that today’s outcome, now that someone has been held to account for what happened, will give them at least some comfort to begin to heal.”
Horrobin claimed he had been acting in self-defence when he threw a punch at Mr Siddall, who he said had deliberately pushed him at the bar and when he later walked through a group made up of Mr Siddall and his friends he “heard something muttered” about him.
Horrobin then went to the bar and said when he saw the group coming towards him he sensed that “something was going to happen” so decided to punch Mr Siddall before the group had the chance to harm him.
This was refuted by prosecutor Sharon Beattie, who said Horrobin was deliberately out for a fight and had been 'picking on the little guy' when he targeted Mr Siddall, who was almost a foot shorter than Horrobin.
The jury was shown CCTV footage from the club which showed Horrobin walk past Mr Siddall on the dancefloor, and push into him with his elbows twice in the space of 12 seconds.
Footage then shows Horrobin being pulled away from the dancefloor by his friend and taken to the bar area.
Five minutes later, the cameras show Horrobin throw a punch at Mr Siddall - then a melee involving the teacher’s friends and Horrobin.