Lumago worked as a customs official before being recruited into the Uganda Army in 1963 by British officers. After undergoing training at the Sudanese Military Academy in Omdurman, he was made a second lieutenant and posted to Moroto. He underwent additional training over the following years and received steady promotions. By 1971 he held the rank of captain, and he was supportive of Colonel Idi Amin's military coup that year. In 1974 he underwent training in the Soviet Union. Under Amin's rule Lumago became Minister of Industry and Power before—at the rank of colonel—being appointed Uganda's High Commissioner to Lesotho in 1975. Operating from Maseru, he also was given responsibility for Uganda's relations with 12 other states in southern Africa. In July 1976 he was in Kenya, and he overheard Kenya Air Force officers on 4 July, discussing plans by Israel to carry out a raid against Entebbe International Airport to free hostages who were held there by Palestinian and German airplane hijackers with the complicity of the Ugandan government. Lumago and Colonel Gad Wilson Toko, who was in Nairobi for non-military reasons, managed to telephone Brigadier Isaac Maliyamungu after failing to reach Uganda Army Chief of Staff Mustafa Adrisi. Maliyamungu, who was reportedly drunk at a night club, dismissed the warning and told both men that since they were acting in civilian capacities they both should not involve themselves in military matters. The Israelis subsequently launched Operation Entebbe, rescuing the hostages and destroying a significant portion of the Uganda Army Air Force. Lumago was recalled from his diplomatic post back to Uganda later that year.