"The verdict is final and cannot be challenged," the source, requesting anonymity, told The Anadolu Agency.
The court also upheld life sentences handed down against 16 defendants, 15-year jail terms for eight defendants, and ten-year jail terms for 35 others in connection with the same murder.
A minor was also jailed for seven years in the same case.
"The verdicts are final and will be applied to all defendants," defense lawyer Ahmed al-Hamrawi told AA.
He said the death penalty "is the first to be upheld by an Egyptian court against a supporter of Morsi."
The defendants were convicted of throwing opponents from the roof of a building in the coastal city of Alexandria in the summer of 2013.
The killing took place two days after the army unseated Morsi – Egypt's first freely elected president – following massive protests against his one-year rule.
Egypt's army-backed authorities have since launched a wide-ranging crackdown on supporters of Morsi and his embattled Muslim Brotherhood group, detaining thousands and killing hundreds.
Egyptian authorities have also branded the Brotherhood a "terrorist" group on claims that it condones violence, an allegation dismissed by the movement, which says it is committed to peaceful activism.
