Ghazali, in his early 60s, was once head of his military's powerful political security branch and one of Syrian President Bashar Assad's most trusted generals.
There was no official government comment and the circumstances of his death remain unclear.
Director of the Britain-based Syrian Observatory for Human Rights Rami Abdurrahman said Ghazali died nearly two months after he was admitted with a head injury. Abdurrahman said Ghazali had been clinically dead for weeks, quoting informed medical officials in the hospital.
Reports at the time of Ghazali's injury said he was beaten by the bodyguards of another Syrian general, in a dramatic escalation of a political dispute.
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The reports said the disagreement between the two generals started after Ghazali's men were not allowed to play a bigger role in a government offensive against opposition fighters battling the government.
Lebanese media reported that both Ghazali and his rival general were sacked. Reshuffles in Syria's security and military apparatuses are generally not made public.
Ghazali kept the post until 2005 when Syrian forces had to withdraw from the tiny Arab country, ending nearly three decades of military presence following massive anti-Syrian protests after Hariri's assassination earlier that year.
In 2005, a UN probe concluded that high-ranking Syrian and Lebanese security officials, including Ghazali, plotted the assassination of Hariri.
A UN-backed tribunal is currently trying five Hezbollah members in absentia over Hariri's assassination. Both Damascus and Hezbollah have strongly denied involvement.
With Ghazali's death, several people accused by anti-Syrian Lebanese politicians of being involved in Hariri's killing have died.