Parthenius III of Constantinople was an Orthodox prelate who served as the Ecumenical Patriarch from 1656 to 1657. Born in Mytilene, he previously served as the metropolitan of Chios. During his brief tenure, he engaged in theological disputes regarding the Confession of Faith of Petro Mohyla and supported the Tsardom of Russia. His political involvement led to accusations of treason by the Ottoman authorities, ultimately resulting in his execution for refusing to renounce his Christian beliefs.