Titanic and City Tours managing director Sean Donnelly, 50, had denied a charge of assault occasioning actual bodily harm by punching an employee of Belfast City Sightseeing.
He claimed he was taunted and spat at by staff from a competitor company.
One of Donnelly's workers, James Moore, was also convicted of common assault.
The victim, Kevin Boyle, claimed his nose was broken in the incident on 11 May last year.
Donnelly, of St James' Park in the city, claimed he had been on the streets to try to stop aggravation between the rivals.
He told Belfast Magistrates' Court that his firm had signed up to a code of conduct following meetings with City Centre Management and the Department of the Environment.
According to Donnelly's account, Mr Boyle and a colleague approached him and started to taunt hum.
"They said 'Stick your code of conduct up your hole'," the tour boss claimed.
Donnelly alleged that he went to their manager in a bid to get him to intervene, only to suffer further abuse.
The court heard claims that Mr Boyle spat in his direction, started to film him on a phone and tried to coax him into striking out.
"I just got frustrated and tried to grab the mobile phone, and I pushed him. That's all I did," he said.
Accepting Mr Boyle "stumbled" to the ground, he denied punching him at any stage.
Donnelly also revealed that he had suffered a minor stroke just days before the incident.
It was claimed that Moore, 30,  of Rathvarna Park in Lisburn, County Antrim, punched and kicked Mr Boyle after arriving at the scene on Callender Street.
He disputed the allegations, insisting instead that he only told the victim to lie on the ground until the situation calmed.
"I was making sure there was nothing more going to happen because of Squirt (Donnelly) having taken a stroke," Moore told the court.
"I didn't want anything more happening to him."
Despite both defendants denials, the judge convicted both of the charge against them.
They were released to return for sentencing next month.
A bus tour company boss has been convicted of attacking a rival employee during an alleged row over a code of conduct for operators in Belfast.