John McLay, 38, who was convicted of stabbing to death 27-year-old Stephen McDermott, was found dead at his home on January 3 . It is understood he died on New Year's Day.
Police said the incident was not being treated as suspicious.
McLay's death has devastated supporters who have promised to continue fighting to clear his name. He had recently told supporters he had "felt let down by the (legal) system".
The Glasgow-based Miscarriages of Justice Organisation (MOJO), which has been supporting his efforts to clear his name, described his death as a "scandal."
McLay shocked other users of the social networking site Twitter with comments shortly before his death at home in Airdrie, North Lanarkshire. His last words were: "The End."
He was 17 when he was sentenced to life for killing Mr McDermott outside his home in Glasgow in February 1992.
Twenty-one years later he said he was determined to prove he was the victim of a miscarriage of justice. Seven affidavits at the centre of his case, including one from a prison officer, said his co-accused Stephen Harkins had bragged about being the real murderer before his death.
McLay, who has a 22-year-old son, had previously admitted he had tried to kill himself three times as a result of "the torment of what happened". He said last year: "I will fight my case until my dying breath and will leave no stone unturned. I am prepared to take a lie detector test if necessary."
MOJO told supporters in a message: "It is with great sadness that we are informing you all that John McLay McIntosh ... unfortunately he felt let down by the system."
Co-project manager Paul McLaughlin said: "I was very close to John and it is a disgrace that anyone should have been in John's position. All the evidence shows he is an innocent man. It's soul-destroying. All he needed was someone in authority to listen to him.
"The danger was always whether John could cope with continuing. We knew how fragile he was. He had so much going on in his head and it was destroying him."
McLay and his co-accused blamed each other for the murder, with both said to have been "full of jellies" - a reference to the drug temazepam - at the time.
The trial judge, Lord Prosser, told the jury that there appeared to be substantial evidence against Harkins, who had already used his knife on another man that night.
Only one person had stabbed Mr McDermott. But there was also blood on a distinctive jacket said to have been worn by McLay.
The jury found the murder charge against Harkins - then 22 - not proven, while McLay was found guilty. Subsequent sworn statements that Harkins had admitted sole responsibility for the murder before and after the trial were deemed "hearsay evidence".
McLay was not allowed to use them in an appeal that subsequently failed.
However, in December 1997, then Scottish Secretary Donald Dewar referred the case to the Court Of Appeal in a landmark ruling that resulted in the statements being considered.
That evidence included a statement from prison officer William Blake who said Harkins told him McLay was serving life for a murder he had not committed.
But it did not occur to him to tell senior officers immediately and he refused to give an affidavit at first as he feared harm would come to him.
He eventually made a statement after Harkins died in January 1999.