This Diocese was formed out of the subdivision of the Diocese of Mount Kenya in 1975, with its headquarters in Kiambu. The Rt. Rev. Obadiah Kariuki was its first Bishop. He retired in 1976 and was succeeded by the Rt. Rev. Sospeter Magua, who was consecrated on 31 October 1976. The Rt. Rev. Eshbon Ngaruiya moved with Bishop Kariuki to remain his Assistant Bishop and continued to serve in this capacity under Bishop Magua.