Since March he had been privately battling recently diagnosed lung cancer on top of a failing kidney and the legacy of the debilitating auto-immune disease, Wegener's granulomatosis, that had been his constant companion for the past 23 years, but still his trademark sense of humour did not falter.

"He was perched on the side of the bed, oxygen going into his nose and a lot of drugs on board at this point, but he was incredibly lucid" said Tony Jones, host of ABC TV's Q&A, and one of Colvin's closest friends at the national broadcaster.

"Suddenly he laughed, and cut across everyone else, and said, 'it's all been bloody marvellous, put that down, because my life has been bloody marvellous'. And he said to put it out at 1pm on the day he died."

That tweet duly went out at lunchtime on Thursday, a last message to his 103,000 Twitter followers from the man described by Jones as "our greatest ever broadcaster".

Colvin, he said, was deeply erudite - "The best-read person I know" - as well as being "immensely funny" with an almost encyclopaedic knowledge of satire. Even in his last days a copy of the British satirical magazine Private Eye was by his bedside.

Above all else was Colvin's indomitability, Jones said. "His resilience in the face of this terrible illness has been extraordinary; we are talking decades where he has managed to continue to get up, often in pain, and go to work and broadcast ... he was the smartest, best-informed guy on radio and listeners will respond with terrible grief and sadness that this voice they had become used to for a very long time has been taken away from us."

Colvin, 65, spent the past two decades of his more than 40 years at the ABC hosting the evening radio current affairs program, PM, having had to abandon a career as a foreign correspondent after picking up a rare virus in 1994 while covering the aftermath of the genocide in Rwanda.

It was during his foreign correspondent years, on assignment for Four Corners along the Angolan-Namibian border, that he ran into Nick Warner, who now heads Australia's Secret Intelligence Service (ASIS).

Late last year Mr Warner launched Colvin's memoir, in which the broadcaster told the story of trying to unravel the secrets of his father John, who had been a spy for MI6, Britain's overseas intelligence agency.

Mr Warner told Fairfax Media that Colvin had won widespread esteem as, "a person and a voice you could trust ... like everybody else in Australia who is interested in the world of current affairs, I listened to him every night as I drove home. And as he observed in his book, unlike his father, he never took sides, he was interested in presenting the facts, not pushing a particular line."

He also paid tribute to Colvin as, "a modern polymath, a font of knowledge, who'd read every book you had ever thought about reading".

After being grounded by ill health Colvin became an expert navigator of the new gateways opened up by digital technology. Jenny Brockie, host of the SBS Insight program and another of his long-time friends and former colleagues from the ABC, remembers his delight when he first discovered Twitter, during one of his periodic confinements in hospital.

"It's just made for people in hospital," he told her.

"Mark epitomised all the best of old-school journalism - fairness and curiosity and intellectual rigour - and he valued the notion of being widely read, he was interested in such a broad range of things - music, comedy, politics, art - and it all contributed to him being a great journalist," Brockie said.

Tributes poured in for Colvin in the hours after his death from Prime Minister Malcolm Turnbull, Opposition leader Bill Shorten, former Attorney-General Philip Ruddock, ABC head Michelle Guthrie and many others from the worlds of politics, current affairs and the arts.

ABC news director Gaven Morris said Colvin was, "one of Australia's finest journalists, admired and respected by his workmates and audiences alike for his intellect, wit and absolute integrity".

The host of ABC TV's Media Watch, Paul Barry, said Colvin's death was, "the passing of an era: he was straight, he was fair, he didn't cut corners, he was brutally honest and there were very few like him then, and even fewer nowadays".

"He never bemoaned his appalling bad luck - he was a brave man."

Among the gems the Oxford-educated Colvin left behind was the two-part interview he recorded late last year with Richard Fidler, who hosts ABC radio's Conversations program.

"He was just one of those people about whom the British would say, he had a hinterland", Fidler told Fairfax Media on Thursday.

"He had this beautiful mind, full of history and literature and music, it swum around in his head all the time, and informed everything he did, but he wore all his education very lightly.

"It gave him ballast against cynicism. He had seen terrible things, a pile of corpses in Iran, he saw what happened in Rwanda but it did not make him cynical.

"Mark just got better and better the older he got. He brought the best and oldest values of journalism into the digital age," Fidler said.

Colvin is survived by his mother, Anne, wife Michelle, and sons Nicolas and William.