But a visit to an oncologist three weeks ago revealed the cancer had spread into his bones.
Further scans revealed malignant tumours in his right hip, parts of his spine, his right shoulder, his right arm and his brain.
"I asked the doctor, 'How long?' and he goes, 'Two months'."
"We knew it was bad but this really was a shock and a real slap in the face."
Mr Major came up with the roast idea when a mate said he didn't want to organise his funeral.
Dozens have signed up for the event, with some coming from the United States and Australia.
They won't be short of material to choose from to give him a hard time.
Mr Major won a fashion-in-the-field event dressed in full drag at a race meeting and ran for the Tauranga mayoralty in 2001, campaigning on "major" change.
He won 1771 votes, which he said was probably thanks to the variety of outfits he had made himself.
He also had a stint as a semi-pro boxer but quit "because I was too bloody fat", and has hammed it up in Tauranga theatre productions.
The roast rules are simple: no boring stories, soppiness or crying. Abuse must be delivered in less than a minute. And, of course, fancy dress is compulsory. "It's about having a bloody big laugh. We have a gong so if anyone tries any sentimental crap, we'll just whack it."
Mr Major has no bitterness or regrets but there's a hint of sadness at some of the things he hasn't done.
He wanted to see his rugby-mad stepson Cory get an invitation to the All Blacks' changing room and to attend the Wellington Sevens in one of his self-made costumes.
"And to get this place paid off," he said, pointing to his Tauranga home. "I wanted to leave my wife financially unburdened."
Mr Major said New Zealand men needed to take a less laid-back approach in monitoring their health.
He blamed the "slight niggles" in his late 30s on his physical work, not knowing they were the first signs of cancer.
"I was one of those blokes [who] never went to the doctor for anything - I really should have."
But his illness had helped him to realise what was important in life.
He and his second wife Ailey have travelled often and enjoyed time with their extended, blended family.
Mr Major's parents shouted him a trip to Italy to visit his brother. They visited Venice and Mont Blanc but came home last week after he spent time in a Milan hospital when his condition worsened.
"It's just really opened my eyes to how much spending time with a person you love really means.
"Life is about happiness and memories, not material things."
Mr Major hopes to be around for Christmas "and beyond" but doubts he'll make his 50th birthday next July.
He is donating his body to the Auckland School of Medicine.
