A family spokesman has described Muhammad Ali's cause of death as "septic shock due to unspecified natural causes".
Ali died on Friday at 9:10pm, spending the last hour of his life surrounded by his family, spokesman Bob Gunnell said at a press conference in Scottsdale, Arizona, on Saturday.
The funeral for the legendary boxer will be held on Friday in his hometown Louisville, Kentucky, Gunnell said.
Ceremonies will start with a funeral procession through the streets of Louisville, he added.
The funeral, scheduled for 2pm at the KFC Yum! Center, will be open to the public and will be streamed online, Gunnell said.
"Ali was a citizen of the world, and he wanted people of all walks of life to be able to attend."
The spokesman said the eulogies will be given by former US President Bill Clinton, actor Billy Crystal and journalist Bryant Gumbel.
'Strength of his spirit'
One of Ali's daughters described her father's last moments on social media by saying "his heart wouldn't stop beating for 30 minutes after all of his other organs failed".
"No one had even seen anything like it," Hana Ali wrote on Instagram.
She said the family was surrounding Ali, hugging and kissing him, holding his hands and chanting an Islamic prayer while his heart kept beating as his other organs failed.
She called it a "true testament to the strength of his spirit and will".
Ali was initially hospitalised in the Phoenix area on Monday.
Soon after retiring from boxing in 1981, rumours began to circulate about the state of Ali's health.
His speech had become slurred, he shuffled and he was often drowsy.
He was eventually diagnosed with Parkinson's disease in 1984, at the age of 43.