McKinnon’s family plans to travel to New Zealand for his shooter’s sentencing.
Garson also entered a guilty plea to a charge of threatening to kill McKinnon’s fiancee, Canadian midwife Bianca Buckley.
The pair had been sleeping in the caravan at the Te Toto Gorge car park in the early hours of August 16, 2019, it was said at the time.
A gunman burst in about 3.20am and fired multiple shots in what police believed was a random attack.
McKinnon was shot dead, and Buckley fled down a rugged coastal road to seek help from a farmhouse.
McKinnon’s body was later found in the rented camper van, about 70 kilometres away in Gordonton, near Hamilton.
On Wednesday, members of McKinnon’s family in Australia watched Garson admit the charges through an audiovisual link to the court.
Justice Pheroze Jagose remanded Garson in custody until his sentencing on December 9.
The sentencing date was chosen so McKinnon’s family could come to New Zealand to attend, Crown Prosecutor Jacinda Hamilton said.
Garson had one supporter in court, and called out “love you my, bro” as he was led from the courtroom.
But the woman Garson threatened to kill is tired of hearing about him.
“I’m just glad he has finally stopped wasting everyone’s time by pleading guilty,” said a statement from Buckley, issued through victim advocate Ruth Money.
“I don’t think I need to spell out the magnitude of the impact that murdering my future husband before my eyes and then threatening to kill me has had on the life of myself and our loved ones … No punishment he ever receives will balance out his wrongdoing.”
McKinnon, from the western Victorian surf town of Nirranda and Buckley got engaged around Christmas in 2017.
His older sister Emmeline McKinnon described him as a loveable character who enjoyed travelling.
“He suffered from a bit of the old restless soul syndrome, he was a hard worker, a brilliant musician and an amazing surfer,” she said.
In court, Justice Jagose warned Garson he was now subject to the three strikes law.
That means any more serious violent offending will earn him a prison sentence without parole or early release, and another murder conviction would result in life imprisonment without parole, unless it would be manifestly unjust.