He was a school teacher until 1863, when he entered the ministry.
The CMS was impressed by Johnson's potential, and sent him to its Yoruba mission in Nigeria, first in Lagos and then in Abeokuta. He was unsuccessful as a missionary, perhaps because of his rigid morality, and in 1880 was instead appointed pastor of the Breadfruit Church in Lagos.[1]
In 1900, Johnson was consecrated a bishop, to serve as an Assistant Bishop in the Diocese of Western Equatorial Africa with oversight of the Niger Delta and Benin territories,[3] holding this post until his death in 1917.
He believed in a puritan, evangelisticChristianity, but was hostile to other aspects of European culture which he felt were not suitable to Africa.[1]