The Clean Up Australia founder was on Friday honoured by hundreds at a state memorial service inside Sydney's iconic Opera House.

Mr Kiernan died in October, aged 78, after being diagnosed with cancer in July.

Clean Up co-founder Kim McKay said her friend and 1994 Australian of the Year had left a long-lasting legacy both in Australia and around the world.

"He was anything but ordinary," Ms McKay told those gathered.

"He proved an individual can make a difference."

Australian rock singer Jimmy Barnes performed at the service, while Mr Kiernan's daughters Sally and Pip and NSW Premier Gladys Berejiklian read tributes.

"The powerful lesson of dad's life is that greatness is within reach of all of us," Pip Kiernan said.

"My dad showed us all that just like the oceans he loved, human potential is limitless."

Sally Kiernan described him as a "cheeky rascal" and "loveable rogue" who always aimed high.

He was remembered by Ms Berejiklian as "one of a kind".

"(He was) a patriot and environmentalist and a true humanitarian who truly left the world a better place," she said.

Blanche d'Alpuget, the wife of former Australian prime minister Bob Hawke, described Mr Kiernan as "the most gorgeous man" and "wonderful Australian".

"His legacy for the world is something that will go on for decades and decades," she told reporters.

Mr Kiernan founded Clean Up Australia 30 years ago as Clean Up Sydney Harbour after becoming dismayed by the pollution he saw as he sailed the world's seas.

The following year his idea went national, before going global in 1993.

He received several honours including a Medal of the Order of Australia in 1991 and in 1995 he was appointed an Officer of the Order of Australia.

He is survived by his wife Judy, daughters Sally and Pip, and son Jack. The family has requested people donate to Clean Up Australia in lieu of flowers.

Australian Associated Press