Praising his friend of more than 30 years as a "superb satirist", fine painter and entertaining contrarian, Mr Turnbull expressed his dismay over the News Corp cartoonist's premature death at 61.

"I can't believe that Bill Leak is dead," he posted on Facebook. "Who had more life, more energy than him? So many more cartoons to draw, paintings to paint, politicians to satirise - so many more lives to enhance with his wit, his brilliance, his good friendship."

Mr Turnbull said he and wife Lucy met Leak while he was drawing courtroom illustrations of the famous Spycatcher trial. Mr Turnbull was the barrister who defeated a British government suppression order on the publication of a memoir by former MI5 spy Peter Wright.

"We were young, filled with mischief and confidence and delighted to shake up the British establishment," Mr Turnbull reminisced on Friday.

"And right through his far too short life, Bill was always a good-humoured sceptic of anybody and anything in authority; he was a superb satirist."

Leak painted Mr Turnbull's portrait for the 1994 Archibald Prize, winning the people's choice award in 1994. At the time, he had also been commissioned to paint the official portraits of then Governor-General Bill Hayden and Prime Minister Bob Hawke.

"Yes, art is long and life is short, but it shouldn't be this short," Mr Turnbull wrote. "Bill should have grown old and even more wiry, like Norman Lindsay, and kept painting into his 80s and beyond as Lloyd Rees did and John Olsen is doing today."

Leak died on Friday morning at Gosford Hospital following a suspected heart attack. He won nine Walkley awards for his work, and had on Wednesday launched a book of his most popular cartoons in The Australian.

In recent years Leak was known for controversial cartoons about Indigenous Australians, Islam and homosexuality, and was a prominent campaigner for free speech and reforms to Australian anti-discrimination laws.

Attorney-General George Brandis said he was "shocked and deeply saddened" by Leak's death, having met with the cartoonist only recently to discuss free speech.

"He was a brilliant cartoonist, a highly accomplished portrait artist, and a great champion of freedom of speech," Senator Brandis said.

"He did what great political cartoonists must do, shining a light on hard issues in a way that was witty, penetrating, and brave. His humour was sharp but never cruel."

Former prime minister Tony Abbott also heaped praise on Leak as a "superb artist, fine mind [and] brave soul".

"No one better illustrated the great truth that a picture is worth a thousand words," Mr Abbott wrote. "We are all aesthetically, culturally and even spiritually impoverished to lose this wonderful man."

Immigration Minister Peter Dutton said Leak combined "amazing talent" with wit and honesty. "He was an honourable man," Mr Dutton said.

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