Rev’d Obadiah Kariuki was made assistant Bishop of the Diocese of Mombasa at Namirembe Cathedral, Kampala by The Most Rev’d Geoffery Fisher on 15th May 1955.

In 1960 the large Anglican diocese of Mombasa was divided into four dioceses namely Mombasa, Fort Hall, Nakuru and Maseno. The Rt. Rev’d Obadiah Kariuki was consecrated as the first bishop of Fort Hall Diocese now in the church of Province of the East Africa and in 1960 and later enthroned In January 1961. Fort Hall, as it was called, then covered Central Province namely Kiambu, Murang’a (Fort Hall), Nyeri Embu and Meru. The Diocese of Fort Hall was then later renamed to Diocese of Mt. Kenya in 1963 when Kenya attained her independence.

In 1975 the diocese of Mt. Kenya was divided into Mt. Kenya East and Mt.Kenya South. The first Diocesan bishop of Mt. Kenya east was Rt. Rev’d David Gitari, therefore Rt. Rev’d Obadiah Kariuki was then the first Bishop of Mt. Kenya South. The Diocesan Headquarters were in Murang’a.

The major work that the first diocesan bishop had was to evangelize having in mind that the newly diocese had no workers in place yet. Having to work with people from abroad, running the diocese became a huge task and therefore He, Rt. Rev’d Obadiah Kariuki, had to train his own. To make his administrative work easier, He sub-divided the diocese into 3 archdeaconries namely, Southern, Embu/Nyeri and Central. In 1971, he chose Rev. Eshbon Ngaruiya as the first Assistant Bishop

Due to his ailment, he was forced to take an early retirement and leave most of the diocesan work to the assistant Bishop, Rt. Rev’d Eshbon Ngaruiya. Later on, after working tirelessly to grow the Body of Christ and the church at large he retired, and the retirement service was held on Saturday, 15th May 1976 at Cathedral of St. James and all Martyrs, Murang’a. The Rt. Rev’d Eshbon Ngaruiya continued serving the Christians until his retirement in 1979.