Diego Carbone was in December found guilty of murdering 25-year-old Bradley Dillon in a second trial, after his first conviction was overturned on appeal.
NSW Supreme Court Justice Peter Garling delivered the verdict, finding Carbone had entered into an agreement with his cousin Tony Bagnato to at least grievously injure the man.
The court had previously heard Mr Dillon had been chasing repayment of money his sister lent to a member of the Saint Michael Fight Club.
Carbone was a former member and Bagnato a leader of the boxing and martial arts club, and both knew Mr Dillon from school.
The judge-alone trial heard the pair had lured Mr Dillon into an underground car park in Leichhardt in August 2014, where he was stabbed repeatedly from behind and shot three times as he ran away.
The Crown contends that Carbone - now 30 - played an active role in planning and executing the attack.
He was the one who informed Bagnato of the debt dispute, he scoped out the carpark where the attack would take place, and he armed himself with a knife from the kitchen of his family's restaurant, prosecutor Michelle England said.
He was arrested with scratches on his cheek, and his DNA was found under Mr Dillon fingernails, inferring he was the one who had placed Mr Dillon in a chokehold and stabbed him from behind.
"The murder of Bradley Dillon was a savage and unprovoked killing, following a carefully planned and premeditated ambush of an unarmed man in circumstances where Mr Dillon had no opportunity to defend himself," she said.
However, Carbone's lawyer has argued the agreed intention to harm Mr Dillon was only formed minutes before the attack and that Carbone had no idea the man would end up dead.
"He wasn't responsible for the stabbing, he didn't bring the knife, and he had no idea that his friend was going to draw a gun and kill this man," Mark Tedeschi QC said.
"The fact that (Mr Dillon) died can be attributed entirely to Mr Bagnato."
Citing a letter Carbone had sent to the previous trial's judge saying he had been "led like a dog on a chain" into the conflict, Mr Tedeschi said his client was a man of "very meagre intellectual means".
"That doesn't excuse anything," he said.
"But it does go to explain why ... he would just go along with Mr Bagnato, not perhaps realising what the risks were of a flare-up ... and Mr Bagnato doing something so crazy."
Mr Tedeschi also asked the judge to reduce Carbone's sentence given the charges have been hanging over his head through two trials and more than six years in custody.
The judge earlier heard from Mr Dillon's family about the daily impact his death continued to have on them.
His attackers were "spineless cowards", Mr Dillon's sobbing mother said, noting all of her son's injuries were from behind.
After comforting the distressed woman, one of his sisters, Kellie Dillon, told the court her family had suffered through seven years of relentless waves of grief.
"(Even now) the waves keep crashing ... on Bradley's birthday, Father's Day, Christmas lunch, milestones," she said.
"Everything is a constant reminder that he's missing and things will never be the same.
"The waves will keep on coming forever."
Carbone will be sentenced at a later date.
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