The man, who other news publications have named as John Peter Latorre, was found just after 4.30am on Tuesday outside a home in Buchanan Place, Greenvale, about 20km north of Melbourne.
Mr Latorre, a fruit and vegetable wholesaler, is reported to have links to Melbourne's Italian mafia.
Detective Senior Sergeant Danny Travaglini said the 64-year-old victim was walking out of his garage to his driveway to go to work when he was shot a number of times in the upper body.
"As he exited his premises he was approached by an unknown person, or persons, where he was shot," Sgt Travaglini told reporters on Tuesday.
Paramedics tried to revive Mr Latorre but he was declared dead at the scene.
At least two of his family members were home at the time of the incident with one relative discovering the victim.
Detectives have spoken to Mr Latorre's family but said they were "quite distraught" and were not in a position to provide much detail.
Two women were escorted through police tape at the crime scene by detectives, with one person consoling a visibly upset woman.
Mr Latorre's brother Vincent was seen visiting the scene of the shooting, hugging and standing among a group of people.
Also a fruiterer, he was jailed for more than a decade in 2009 for blackmailing business rivals and squeezing them for hundreds of thousands of dollars.
An inquest in 2007 found Vincent Latorre had either killed or aided in the death of 20-year-old Rocco Iaria, whose body was found dumped in an occupied grave.
Police are yet to formally identify the man, but Sgt Travaglini said potential gang links to the shooting would form part of the investigation.
He said initial inquiries suggested the man was known to Victoria Police.
The crime scene was expanded after initial inquiries suggested a car might have approached from a particular area, police said.
Sgt Travaglini said there was nothing yet to suggest any revenge attacks but warned links to organised crime posed the potential for payback.
"That's where Victoria Police approach such investigations as a high priority ... to ensure we mitigate any further risk," he said.
"We obviously have proactive units within Victorian Police to try and disrupt and impact organised crime to ensure that retaliation and other activities don't occur."
Detectives have ruled out any links between the shooting and a fire at a shop on Glengala Road in Sunshine West on Tuesday morning.
No arrests have been made as authorities look into the background of everyone involved or known to police, who lived in the area or associated with Mr Latorre.
"We will do whatever we possibly can to ensure there's no retaliation if there's anything suggested as retaliation," Sgt Travaglini said.
Police are asking anyone in the area with information or CCTV footage to come forward.
