Diego Carbone, 26, was found guilty last October of murdering Bradley Dillon, 25, who was shot and stabbed in the Leichhardt car park on August 11, 2014.

Carbone gave a thumbs up to his sobbing family as he was sentenced in the NSW Supreme Court on Thursday to 28 years in jail, with a non-parole period of 21 years, while family members of the victim cried and cheered.

Riot squad police were present in the packed court to separate family members of both men, while Mr Dillon's sister wept as Acting Justice Jane Mathews described the drug user's premeditated fatal attack on his "entirely innocent" victim.

"Mr Dillon was shot from behind when he was attempting to run away," she said.

"It was a brutal and completely unnecessary killing."

The court had previously heard Mr Dillon had been chasing repayment of $2000 his sister lent to a member of the Saint Michael Fight Club.

Carbone was previously a member of the boxing and martial arts club.

His cousin, kickboxer Antonio Bagnato, fled the country soon after the murder and is suspected of carrying it out with Carbone.

Bagnato is on death row in Thailand after being found guilty of murdering Sydney underworld figure and Hells Angels bikie Wayne Schneider in a villa, south of Bangkok, in November 2015.

Nadine Dillon told Carbone's sentence hearing her "heart and soul" were ripped out by the senseless murder of her partner, while the victim's mother described the crime as spineless and cowardly.

Australian Associated Press