British East Africa During World War I
In 1912, having completed his mission school education, Kamau became an apprentice carpenter. The following year he underwent initiation ceremonies (including circumcision) and became a member of the kehiomwere age group. In August of 1914 Kamau was baptized at the Church of Scotland mission, initially taking the name John Peter Kamau, but swiftly changing it to Johnson Kamau. Looking to the future, he departed the mission for Nairobi to seek employment.
Initially he worked as an apprentice carpenter on a sisal farm in Thika, under the tutelage of John Cook, who had been in charge of the building program at Thogoto. As World War I progressed, able bodied Kikuyu were forced into work by the British authorities, to avoid this, Kamau moved to Narok, living amongst the Maasai, where he worked as a clerk for an Asian contractor. It was around this time that he took to wearing a traditional beaded belt known as a 'Kenyatta', a Swahili word which means 'light of Kenya'.