His early education was at the Central Primary School, Mbieri, Imo state, where Josiah worked. At the time, they lived at Umunjam, also in Imo state. Through a lot of devotion and hard work, he gained admission into the prestigious Dennis Memorial Grammar School, Onitsha (DMGS). His time at DMGS was quite memorable as he often spoke about it, especially about the joy he had in playing the organ they had over there. From Onitsha, Gabriel went to the Nigerian College of Science and technology in Zaria, where he got his 'A' Levels in Physics, Chemistry, Botany and Zoology. From Zaria, he went to the University of Ibadan, to pursue a career in Medicine. He qualified as a Medical Doctor from the University College Hospital, Ibadan (UCH). In 1962, he went to the Lagos University Teaching Hospital (LUTH), Yaba Lagos. In 1963, Dr Gabriel Ezeilo went to the School of Tropical Medicine, Liverpool. He finished his Diploma in Tropical Medicine and Hyegine (DTM&H) in 1964. Next was a couple of memberships of the Royal College of Physicians, one from Glasgow (MRCP, 1965), and one from Edinburgh (MRCP, 1966). He also worked at the Royal Edinburgh hospital during this period. In 1967, his relentless hard work paid off when he earned an Msc in Physiology from the University of Rochester, New York.