Yassin Hatem Salah Eddin, 24, was in June convicted and jailed by the Cairo Criminal Court on manslaughter charges over the death of 32-year-old activist Shaimaa el-Sabbagh.
The Egyptian court agreed to retry Eddin on his appeal against the conviction.
El-Sabbagh was killed after a masked policeman fired a birdshot in her direction during a peaceful demonstration in January 2015 to commemorate the protesters died during the 2011 revolution that toppled president Hosni Mubarak.
The killing had stoked anger among many Egyptians over perceived brutality of the police. Authorities had initially denied that police had any involvement in her death.
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Rights activists had said the police hampered efforts to save el-Sabbagh's life by preventing an ambulance from passing through the cordon.
The uproar over El-Sabbagh's death had forced Egypt's President Abdel-Fattah el-Sissi to order an investigation.
Hundreds of activists were put in jail and are tried over protesting without permit.