2012 champ James needed staples in his head after being hit with a glass bottle and punched on a night out.
The defendant, who had 12 previous convictions, was sentenced to five and a half years for wounding with intent in court this week.
It was alleged that the "unprovoked" attack followed claims James had got together with the attacker's former girlfriend.
Prosecutor Nick Dry said at the sentencing: "James Arthur and his group were walking towards the beer garden when without warning or provocation [the defendant] smashed a glass forcibly on the back of his head.
"As he stumbled forward from the incident the defendant followed up with a punch."
"He claimed he had attacked him because he had slept with an ex-girlfriend some time ago," he continued."He said he had lost it and whacked him as hard as he could.
"He denied using a glass and said he had gone into a rage when Arthur smirked at him."
In sentencing, the judge told the accused: "It's clear from your record that you are someone who has difficulty controlling your temper.
"You went after James Arthur and attacked him from behind forcefully with a glass you had in your hand and followed it up with a punch."