Zakka was known for his involvement in ecumenical dialogue. He was a president of the World Council of Churches and also a prolific author. He was an observer at Second Vatican Council before becoming metropolitan bishop of Mosul. At the time of his election as patriarch, Mor Severios Zakka was serving as the archbishop of Baghdad and Basra. As patriarch, he established a monastic seminary, met with Pope John Paul II during the Roman Pope's visit to Syria in 2001, and installed numerous metropolitans, including Baselios Thomas I as Catholicos of India. He celebrated his Silver Jubilee in 2005.