Somare was PNG’s first prime minister following the nation’s independence in 1975 and was known as the Grand Chief and father of the nation.
He had other stints as leader, serving a total of 17 years in that role before retiring from politics in 2017.
He died early on Friday morning after being diagnosed with late-stage pancreatic cancer, a family statement said.
“Sadly, pancreatic cancer is one of the most aggressive cancers that are rarely detected early. We as a family had only two weeks to look for possible treatments for our father,” a statement from his daughter Betha Somare said.
“Sir Michael was a loyal husband to our mother and great father first to her children, then grandchildren and great granddaughter.
“But we are endeared that many Papua New Guineans equally embraced Sir Michael as father and grandfather,” the family statement said.
Australian Prime Minister Scott Morrison tweeted his condolences on Friday morning saying Somare had been the founding father of democratic and independent PNG and had been “a great friend to Australia”.
“My heartfelt condolences to his family, Prime Minister Marape and the people of PNG. Australians stand with you in this time of sadness. May he rest in peace.”
Somare and his wife Veronica had been preparing to go overseas for treatment, his family said earlier this week but after assessing options had placed him in the best palliative care available in PNG.