The assault happened in April 2016, when the man was sitting at the wheel of his parked car when Macdonald approached him.
Macdonald asked the man if he "had a problem" then punched him in the face through the open car window.
He shattered the victim's nose and covered his friend - who was sitting in the passenger seat - in blood. He tried to avoid the attack, only to receive more punches to his body.
Judge Mackintosh decided the victim had done nothing to provoke the sudden attack - as he was just waiting by his ute to collect a friend from a party in Hastings.
"It happened so quickly, I wasn't expecting it. It was completely unprovoked," the victim said at the time.
Macdonald then pulled the keys from the ignition, smashing them on the road before leaving the area.
At last year's sentencing, Macdonald's lawyer Matthew Phelps told Judge Bridget Mackintosh there was "not a specific intention to injure" and said Macdonald was remorseful for his actions, putting it down to "moderate offending".
Phelps told the judge a conviction would mean Macdonald would not be eligible for a visa to the US and would "all but extinguish his prospects of a career in music".
Macdonald's career was on the up after associating with the likes of Snoop Dogg and Wiz Khalifa.
In 2016, his debut album Underestimated sat in the iTunes top 10 for more than a week, at one point toppling Drake from the number one spot for New Zealand album sales.
Macdonald was the first independent artist in the Southern Hemisphere to release a collaboration with Snoop Dogg.
