Zallum was born in 1924 in the city of Hebron (al-Khaleel) in Mandatory Palestine. By the age of 15, he acquired his elementary education from al-Ibrahemia school in city of al-Khaleel. For a higher level of education, his father decided to send him to pursue his education in Fiqh (Islamic jurisprudence) at Al-Azhar University in Cairo in 1939. He was appointed as a teacher in 1949 to the schools of Bethlehem for a period of two years. Zallum wrote a book titled How the Khilafah was Destroyed, which explains in great detail the events that forced the fall of the Ummah of Muhammad. He recounts several instances that contributed to the historical event and his book offers lessons to prevent the same pitfalls from reoccurring.
In 1951 he moved to al-Khaleel and worked as a teacher in Osama Bin Munqiz School. Here he met Taqiuddin al-Nabhani in 1952. He joined Hizb ut-Tahrir in 1953. After the death of Taqiuddin al-Nabhani in 1977, Zallum was chosen to be the global leader of Hizb ut-Tahrir. He remained the head of Hizb ut-Tahrir until he resigned on March 17, 2003. Zallum died on April 29, 2003.