Ian Kiernan, an environmental campaigner who grew to international fame for his work and as a yachtsman, has died aged 78 after being diagnosed with cancer in late July.

He is survived by his wife Judy and two daughters Sally and Pip.

Clean Up Australia co-founder Kim McKay said Kiernan "lived life hard and lived it well".

"It's quite a shock to a lot of people because Ian was only diagnosed with the cancer [quite recently] and it took hold of him quite rapidly," Ms McKay told the ABC.

"He was a larger than life figure, and when larger than life figures leave us in Australia there is a void."

Clean Up Australia said its founder's guidance and humour would be missed but "it was his greatest wish that the work he inspired continues".

"Ian believed that Clean Up belongs to the millions of volunteers who have taken to their streets, beaches, parks, bushland and waterways to remove the rubbish that is bothering them," the organisation said in a statement.

"More recently this has extended to the thousands who take actions such as saying NO to a plastic bag at the checkout, refusing a single use item, or who join us via our social media campaigns.

"Fondly nicknamed by Phillip Adams, 'The Greatest Garbo since Greta', Ian Kiernan's greatest legacy is the creation of an informed, concerned, committed, and involved community — sharing his passion for the safeguarding of our most precious asset, our environment."

Prime Minister Scott Morrison said he met the campaigner "a number of times over the years".

"His passion for our oceans, which started all of this for him, and Australia's coastal lifestyle, in particular, is something that I think struck a real chord with all Australians," Mr Morrison said.

"The thing that I think Ian did more than anything else was tap us all on the shoulder and say, 'hey, we've got to take care of this — this is our responsibility to do this, it's not the government's, it's ours, as Australians'."

NSW Premier Gladys Berejiklian said Mr Kiernan's family has accepted an offer for a state memorial service.

The idea for Clean Up Australia Day came to Ian Kiernan when he sailed around the world and saw an ocean teeming with rubbish. ( Supplied: Australian of the Year )

The birth of a movement

Born on October 4, 1940, Kiernan grew up around Sydney's harbour and beaches where he learnt to swim, fish and sail.

Educated at Scots College and The Armidale School in northern New South Wales, he went on to work in the construction industry, specialising in historic restorations.

Awards His environmental campaigning efforts were recognised with numerous Australian and international awards, most notably: 1991 Medal of the Order of Australia (OAM)

1991 Medal of the Order of Australia (OAM) 1993 United Nations Global 500 award for the Environment

1993 United Nations Global 500 award for the Environment 1994 Australian of the Year.

1994 Australian of the Year. 1995 Officer of the Order of Australia (OAM)

1995 Officer of the Order of Australia (OAM) 1999 World Citizenship Award

1999 World Citizenship Award 2001 Centenary Medal

But it was his love of sailing that led to his remarkable career as a global environmentalist founding the "Clean Up Australia" and "Clean Up the World" campaigns.

In 1986, the then 44-year-old represented Australia in the BOC solo around-the-world yacht race.

He finished sixth out of a fleet of 25 yachts from 11 nations, but set an Australian record for a solo circumnavigation of the world.

During nine months at sea, Kiernan was appalled by the amount of rubbish he had seen choking the world's oceans.

On his return, he set out to do something about it, and with the support of his friends organised a community event, "Clean Up Sydney Harbour" on Sunday, January 8, 1989.

It was a huge success, with more than 40,000 volunteers lending a hand.

Ian Kiernan and former ACT environment minister Simon Corbell with a group of students ready to clean up. ( Kathleen Dyett )

The next year, the first Clean Up Australia Day took place, with more than 300,000 Australians volunteering their time to pick up rubbish and help make a difference to the health of their local environment.

In 1991, Kiernan started Clean Up the World. In its first year, more than 30 million people from 80 countries participated.

It has since grown to involve over 40 million people from 120 countries.

In 1994 Kiernan rushed to protect Prince Charles after a man with starter's pistol stormed the stage at an Australia Day event at Sydney's Darling Harbour.

After the "royal assassin" was taken away the Prince continued with his role in the event and Kiernan was awarded Australian of the Year.

Ms McKay, who was sitting with Kiernan's wife on stage, said "he was never afraid of anything and he'd always react to and square up to a problem".

"He jumped up from his chair in the second row, ran around as he saw this man approaching the stage with a — they didn't know it was a starting pistol at the time he was firing, they thought it might have been a gun," Ms McKay said.

Kiernan rushes to tackle a man who fired a starter's pistol twice at Prince Charles. ( ABC News )

A life at sea

A passionate yachtsman all his life, Kiernan competed in more than a dozen Sydney-to-Hobart races, including the ill-fated 1998 race in which six sailors died.

He also represented Australia at the Admiral's, Southern Cross, Dunhill, Clipper, Kenwood and Trans Pacific Cup.

While he sailed on many yachts, one has become synonymous with his name, MARIS. He bought the classic timber yawl in 1971 from famous marine artist Jack Earl on condition he teach him how to cross oceans on it.

Kiernan said on reflection: "He certainly did that. I became a celestial navigator; Jack taught me to practise with my sextant bringing the sun down in a dish of oil."

For nearly 40 years, Kiernan and MARIS were inseparable as he cruised around the Pacific Ocean, competed in Sydney-to-Hobarts, Lord Howe Island races and the single-handed Trans-Tasman race in 1978.

In that event he won Division 1, sailing through Cyclone Hal which sank three other craft.

Kiernan's legacy on Sydney Harbour hit headwinds last year though when the NSW Government cited two drink-driving convictions as the reason for not naming a Sydney ferry after him — favouring Ferry McFerryface and later May Gibbs.

According to a Freedom of Information (FOI) report, Kiernan received more votes than Ferry McFerryface, which is now being labelled as the minister's choice.

Kiernan said he was told in 2017 his name would be going on the ferry.

"I was greatly honoured to have been considered to have my name on it but then to turn it to something like Ferry McFerryface was a big disappointment," he said.