Parker reveals in posthumous memoir Hope, serialised in The Sun newspaper how despite having a problem cannabis habit in his teens, he turned back to the drug for pain relief at the end of his life.
The Glad You Came singer revealed: "There’s not many people who are diagnosed with glioblastoma who reach a year down the line and get their tumour to a stable state like I did. Despite all the trouble that it caused earlier in my life, I honestly do credit cannabis for that."
The singer - who shared two-year-old daughter Aurelia and 18-month-old son Bodhi with wife Kelsey Hardwick - revealed he began to take a few drops of cannabis oil every evening after his diagnosis.
He said: "At the very least I can say it definitely stimulated my appetite, and that’s a good thing for someone going through cancer treatment. Perhaps even more importantly, it’s made me laugh at things."
But Parker admitted that after dropping out of university but before joining boyband The Wanted, smoking cannabis had caused problems in his life.
He revealed: "Over the space of a couple of years I’d gone from casually smoking with my mates to full-on addiction. We would do pretty much anything to get high."
Parker confessed he was "ashamed" to admit he had even stolen money from his parents to buy drugs.
But he managed to turn his life around after auditioning for The Wanted in 2008.
Parker joined his bandmates on tour in March for a special appearance alongside them on stage and, in photos that Max George shared from their time together, he was shown in a wheelchair.
He had been forced to pull out of tour dates to undergo cancer treatment, but joined George, Sykes, Kaneswaran, and McGuiness in surprise appearances at shows.
In December last year, Parker spoke at an all-party parliamentary group on brain tumours via video-link.
"I’m staggered they can find a cure for COVID within a year but, for decades on end, they haven’t found better treatments let alone a cure for brain tumours," he said.
“Why is it taking so long for clinical trials to come through?”
Parker had undergone several rounds of chemotherapy and over 30 radiotherapy sessions, and revealed last week that he had written a book about his cancer battle.
He told fans: "My book is not about dying: It's a book about living. It's a book about finding hope in whatever situation you're dealt, and living your best life no matter what."
He also appeared in a Channel 4 documentary in 2021, called Tom Parker: Inside My Head.
Watch: Ed Sheeran reportedly helped out with Tom Parker's medical bills as he battled cancer