He studied Philosophy and Theology in St. Thomas Aquinas Seminary, Nairobi.
[1][2] He graduated from St. John Fisher University (at that time "St. John Fisher College") in Rochester, New York State, in the United States with a Bachelor of Arts degree in Religious Studies.
[1][2] While priest of Nakuru, he served in several roles including as:[2] On 17 March 1983, Pope John Paul II appointed Father Peter Joseph Kairo as the founder bishop of the newly erected Diocese of Muranga, which was peeled off from the Archdiocese of Nyeri on the same day.
[1][2][3] On 21 April 1997, Pope John Paul II appointed him the Bishop of the Diocese of Nakuru.
[1][2] After over 8 years of service as the Archbishop of Nyeri, his application for retirement based on his age was accepted by Pope Francis, effective 23 April 2017.