Kevin Thomas said he would be scattering the ashes of the 20-year-old, from Chorley, in Lancashire, at the Isle of Man TT races in June.
"That is what he wanted me to do - he lived for racing," said Thomas.
"He had taken to the roads, the crowds had taken to him. He was a petrol head and just wanted to go faster."
Mitchell-Thomas had been racing at the North West 200 for the first time, having signed for the Cookstown BE Racing team.
He crashed during the Supertwins race at Saturday's road races.
"I want to thank the paramedics for trying to save him at the roadside and the organisers for the way they helped me when things went wrong," Thomas added.
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"It was a great event, but saddened by his loss.
"I have lost my best friend - I have lost my son, but he died doing what he wanted to do.
"He did not have a bad bone in his body and nobody had a bad word to say about him.
"He had been doing great things. We did not come here as a big business with a big bank account.
"We came here through hard grit, determination and mostly a desire to win races. I have never seen desire like he had."
Mitchell-Thomas and his father had been living in a small caravan at the back of the North West 200 paddock area.
Thomas said his son had been loving the event and could not wait for the racing to start.
Mitchell-Thomas finished fourth in Saturday's opening Supersport race.
Thomas said he did not agree with people who wanted road racing banned because of the dangers.
"There are risks in everything you do," he said.
"Mal got knocked off his bike by a car when he was six - he could have been killed then.
"Yes, it is a dangerous sport, but so are other forms of motorsport. So is horse racing.
"I will continue to be involved in the sport because that is what Mal would have wanted me to do."
Cookstown BE Racing owner John Burrows said the team was "devastated" by the loss of its rider.
"Everyone is in a state of shock. Enthusiasm just bubbled out of him and he was a joy to be around," he added.
Jim Gracey, group sports editor of the Belfast Telegraph, described Mitchell-Thomas as "one of the brightest shining young stars who has appeared in motorcycle racing for many, many years".
Gracey added: "He was an absolutely lovely lad.
"Many people here were saying he was going to be the next Guy Martin. He wouldn't have any of it. He said to me: 'I'm the first Malachi Mitchell-Thomas.'
"He told me racing was his be all and end all."
First Minister Arlene Foster and Deputy First Minister Martin McGuinness have expressed their condolences to Thomas's family.
Foster said: "It was with great sadness I learned of the death of Malachi Mitchell-Thomas following a tragic accident at Saturday's North West 200. My thoughts and prayers are with his family and friends and with the wider road racing family at this very sad time."
McGuinness said: "My thoughts and prayers are with the family and friends of Malachi Mitchell-Thomas who tragically lost his life at the North West 200. By all accounts Malachi had established himself as a real up and coming talent and his untimely death is a huge loss to his family, friends and racing team."

Representatives from the west of Norway have been in the isles to discuss how expertise can be shared.
They believe knowledge built up in Scandinavia through work in the oil and gas sector could prove key to the next stage in developing technologies.
Orkney is a major Scottish hub for renewables.
In January, plans for a Â£6.5m research and innovation campus in Stromness in Orkney took a step forward after the organisations driving the project agreed funding.
Highlands and Islands Enterprise and Orkney Islands Council are behind the venture.
The campus is aimed at supporting sectors including marine renewables.
Malachi Mitchell-Thomas, who died at the North West 200 races on Saturday, was a rider of incredible grit and determination, his father said.
[NEXT_CONCEPT]
A partnership is being formed between the energy sectors in Orkney and Norway to look at ways they can work together to develop marine renewables.