Abdelbaset Ali Mohmet al-Megrahi, the only person convicted over the 1988 Lockerbie bombing over Scotland in which 270 people were killed, died on Sunday, his brother told AFP.
“He died an hour ago,” Abdelhakim al-Megrahi said, putting the time of death at shortly after 1.00 pm (1100 GMT).
Doctors had yet to determine the cause of death, he added.
Megrahi, 60, suffered from prostate cancer and was hospitalised for a few days in April before being sent back home to be with his family.
On April 16, Abdelhakim had said his brother’s days “were numbered.”
A Scottish court in 2001 convicted the Libyan of the 1988 attack on Pan Am flight 103 over the town of Lockerbie, but he was released on compassionate grounds in 2009 after doctors said he had only three months to live.
Megrahi had been greeted as a hero on his return to Moamer Kadhafi’s Libya, after having served eight years of a minimum 27-year sentence for his role in the bombing.
The fact that he had survived much longer than the doctors had estimated had provoked indignation in Britain and the United States.
On the second anniversary of the release of the former Libyan intelligence agent on August 20, 2009, the Scottish government insisted its decision to free him had been vindicated.
But British Prime Minister David Cameron criticised the release as a “terrible mistake,” and Deputy Prime Minister Nick Clegg said he would like to see him “back in jail behind bars.”
Most of those killed in the bombing of the Boeing 747 jet headed from London to New York were Americans. All 259 passengers and crew were killed, along with 11 people on the ground.
Megrahi had always maintained his innocence and his brother Abdelhakim has in the past defended him, saying he was “exploited” by Kadhafi’s regime which let him take the blame for a crime he did not commit.
Last August, during the revolution which toppled Moamer Kadhafi, another of Megrahi’s brothers told reporters outside the family home in Tripoli that he was “in and out of a coma.”
Amid the lack of law and order after the revolt which brought armed fighters out onto the streets, his medicine had been looted and no doctors were available, the family said.
In December, Megrahi told several British newspapers in what was billed as a “final interview” that a book being written by investigative journalist John Ashton would clear his name.
“I am an innocent man” he told the papers, including The Times and the Daily Mail.
“I am about to die and I ask now to be left in peace with my family,” he said.
“I will not be giving any more interviews, and no more cameras will be allowed into my home,” he explained. “I am an innocent man, and the book will clear my name.”
Megrahi claimed that he had “never seen” a Maltese shopkeeper whose testimony and identification proved central to the original guilty verdict.
“I never bought clothes from him,” he added. “He dealt with me very wrongly. I have never seen him in my life before he came to court.”
According to Megrahi, US agencies “led the way” in securing his conviction.