Rights groups called for an independent probe into the detention conditions and death of the Islamist, who was ousted in 2013 after a year of divisive rule.
According to State TV, the 67-year-old’s death was due to a cardiac arrest.
“He was buried in Medinat Nasr, in eastern Cairo, with his family present,” said Abdel Moneim Abdel Maksoud, one of his lawyer.
Morsi, also the country’s first civilian president, had appeared “animated” during a hearing in a retrial over charges of collaborating with foreign powers and militant groups, judicial and security sources said.
Another of Morsi’s legal defence team described the moment he received news of his death.
“We heard the banging on the glass cage from the rest of the other inmates and them screaming loudly that Morsi had died,” the lawyer, Osama El Helw, told AFP.