The first bishop and founder of Butare Roman Catholic Diocese was Bishop Jean Baptiste Gahamanyi. He was born in 1913 in Cyeza, Busasamana in the Southern Province. He started his studies at Save in 1928 and was nominated for priesthood at Phophete Adrien School. After his secondary studies, he was sent to Nyakibanda for Philosophy. In 1940, he started his studies in Theology at Kabgayi Minor Seminary and priestly ministry.

He was consecrated Bishop in 1961 at Gitarama Diocese and appointed the Ordinary of Butare on 10th November 1961. He led the diocese through two important religious events and protection of the people of his Diocese. These were: The Second Vatican Council which was held from 1962 to 1965 and the troubles which had stricken the whole nation in 1994. He served as the Bishop of Butare for 34 years from 1961 to 1994. Initially, the diocese comprised almost the whole Southern Province of Rwanda up to 1967. After the nation re-organization, the diocese was confined to the actual Huye and Gisagara districts with 7 civil parishes of Ruhashya, Mbazi, Mukama, Runyinya, Karama, Save, and Kibirizi. Gahamanyi was known for his great affection for education to children and establishing both religious and non-religious educational institutions. He accordingly inaugurated and visited almost all religious and secular schools within his diocese. He contributed in various sectors, for instance, the foundation of seminaries at Save and Nyakibanda where they still are the main center of priestly formation in the Southern Province. Besides his dedication to educational progress, he also worked tirelessly to promote the participation of Rwanda in economic and social fields.

He convinced the church to establish various communitarian projects that aimed at nurturing a self-reliance spirit among the Christians. Initiatives like the construction of secondary schools and hospitals were chosen as cornerstones for both evangelization and development. He died on 20th January 1995, resting from his temporal kingdoms yet to receive the Eternal one in Heaven. His remains are buried in Saint André Cathedral in Butare. His death was not only mourned by the Christians whom he shepherded as their father but also by the government. The President of the Republic of Rwanda, in his message to the Christians, comforted them by confirming that the nation lost a virtuous person and comforter. Gahamanyi had greatly participated in the socio-economic development of the nation, something that many leaders of the nation testified to. For example, the President of the Republic of Rwanda, Mr. Kigeli Pastoral, claimed that the nation will always commemorate the great works done by this Bishop, Bishop Jean Baptiste Gahamanyi.