Makonnen was born George Thomas N. Griffiths in Buxton, Guyana. His paternal grandfather was reputedly born in Tigre, Ethiopia, and taken to British Guiana by a Scottish miner. Makonnen completed his secondary school in Guyana, before leaving in 1927 to study mineralogy in Texas. During the Second Italo-Abyssinian War in 1935, he changed his name to emphasize his African roots. His children are T'Shai R. Makonnen, Desta Makonnen, Lorenzo Makonnen and Sheba Makonnen.