The imprisoned lawyer Ramadan Youssef Ashry, 50, breathed his last in Al-Abadia prison in Damanhour after suffering a sudden heart attack as he was subjected to deliberate medical negligence.
Ashry has been detained in an Egyptian prison since 2014 over political charges.
Ashry is the sixth prisoner who breathed his last in Egyptian custody since the start of the year.
The five other victims include Muhammad Mustafa Badawi, Muhammad Al-Sayyid Al-Mursi, Saad Mahmoud Abdel-Ghani Khader, Mahmoud Al-Didamouni, and Sameh Tolba.
Inhumane detention conditions have long plagued Egypt’s prisons, adversely affecting prisoners’ right to adequate medical treatment and health care.
The International Covenant on Civil and Political Rights states that all persons deprived of their liberty shall be treated with humanity and with respect for the inherent dignity of the human person.