He was wearing a seat belt but the air bags did not deploy and McCallum smashed his head on the windscreen, dashboard, back of the seat and the side of the truck.
Eight parts of his brain were injured.
He had little memory of the party from that night and could not recall why he asked Marsh to drive him the short distance home.
"I should have walked but I didn't want to leave my truck and I didn't want to drive."
He often offered to be the sober driver for his friends and would never consider driving after drinking alcohol.
"I wouldn't even drive if I had a bottle of alcohol like a stubbie."
Police estimated the truck was travelling about 130kmh when it left the road and hit a gate, road sign and fence posts before coming to a stop in a paddock, about 11km from McCallum's house.
Two passengers in the back seat were also injured.
Emergency services arrived at the scene shortly after the crash because a tanker driver had reported the truck weaving across the road after it had just avoided a head on collision with the tanker.
McCallum was airlifted to Dunedin Hospital, where he spent three days in a coma and was discharged just five days after the crash.
But that wasn't the end of his ordeal.
He has since been readmitted many times due to ongoing seizures, which has included five helicopter trips and four comas.
Making the situation more difficult, before a seizure he was likely to wander off in a semi-conscious state, then stop breathing.
An app on his cellphone is used to track him if he does wander off.
Many hours of therapy have helped him learn to walk, eat and speak again but he is still unable to drive or work.
It may be two years before he can work again and it is likely he will never fully recover from his injuries.
Before the crash, he had joined the Gore Red Cross disaster response team but now he was the one that needed help.
"I find it very hard to deal with that emotionally."
He lives with partner Abbie Willoughby and son Harrison (16 months), at the home of his parents, Teresa and Dav.
The experience had been his parents' worst nightmare, he said.
Mrs McCallum said she lived in constant fear about when her son would have another seizure.
"I worry about him stopping breathing and dying during seizures or having one at night, when everyone's asleep.
Twice her husband had given their son CPR and saved his life.
Willoughby said when Harrison saw his father looking unwell he knew what to do, after watching his grandfather giving him CPR.
"It's pretty scary to see a child this young actually going [to his father] and doing CPR," Ms Willoughby said.
The family hoped by sharing their story, young people who drank and drove would change their behaviour.
"Something good has got to come out of this," Mrs McCallum said.
• Marsh, 22, was charged with driving in a dangerous manner, being an unlicensed driver failing to comply with prohibition and three charges of driving with excess breath-alcohol causing injury. In March he was sentenced in the Gore District court to 10 months and 21 days home detention and was also disqualified from driving for three years, fined $300 plus $130 court costs and ordered to pay $4000 reparation to McCallum and $500 each to the other two victims.
