Reece Radford, 26, was stabbed when he intervened after seeing a 17-year-old girl being assaulted in Sheffield city centre on September 26.
He died six days later, and a post-mortem concluded that he died as a result of a stab wound to the chest.
Dereck Owusu, 39, of Strathmore Grove in Wath, has been on trial with 46-year-old Louis James of Sheffield, for almost three weeks.
The pair were found guilty of Reece’s murder after the jury came back with a unanimous guilty verdict at Sheffield Crown Court on Wednesday.
DCI Rebecca Hodgman, senior investigating officer in the case, said: “Owusu and James had been out drinking that night.
“Just before 1am, they were on Arundel Gate in Sheffield city centre when they bumped into a teenage girl they knew, sitting at a bus stop.
“The three of them began sharing some alcohol.
“Shortly after 2.20am, a violent altercation occurred and Owusu punched the 17-year-old girl in the face.
“Reece Radford, who had been out with a group of friends that night, witnessed this assault and stepped in to help this young girl.
“As a result, a fight broke out between the defendants and Reece.
“The three ended up in the road, and Reece fell to the floor where he was subjected to a barrage of kicks from both men.
“Then the assault abruptly ended.
“Reece crossed the road and collapsed on the other side.
“He had been stabbed in the chest.”
After leaving the scene, Owusu later returned to the scene and began to ‘swirl his belt in the air’ before hitting one of Reece’s friends who was on the phone to an ambulance.
The court were told that CCTV operators, having been alerted by police, tracked Owusu and James through the city centre.
The pair were arrested a short time later on suspicion of attempted murder.
This was upgraded to murder following Reece’s death.
The murder weapon - a knife - was discovered during searches of a drain on Shude Hill in the city centre on October 1.
DCI Hodgman added: “I would like to offer my sincere condolences to Reece’s family.
“To lose a loved one in such tragic circumstances has been devastating.
“Throughout their trial Owusu and James have both claimed they had no idea how Reece came to be stabbed during that fight.
“The jury saw through those lies.
“Finally, I would like to thank the team of officers for their dedication to this case to ensure justice for Reece and his family.
“From the swift response on the night of the attack, through the searches for the hidden murder weapon and beyond.”
The pair have been remanded into custody to be sentenced on May 4.