Studied at St George's Hospital, where his brother, Henry Charles Johnson (qv), was for many years Surgeon. He acted as assistant to Robert Lee, Obstetric Physician to the Hospital, reporting his lectures and cataloguing his pathological specimens, and on qualifying he started practice in Arlington Street with the view of becoming an obstetrician. But at the age of 22 he accepted an offer to accompany the blind James, Viscount Cranbourne (1821-1865), eldest son of James, second Marquis of Salisbury (1791-1868), and elder brother of Robert, third Marquis of Salisbury (1830-1903). Johnson travelled with Viscount Cranbourne to the principal blind schools of Europe, including Russia, before there were railways. On his return he continued his attendance upon Viscount Cranbourne throughout his life. He did not return to medical practice, but, aided by the Cecil influence, devoted himself to the welfare of the blind and deaf and dumb. The MD Lambeth was conferred upon him in 1850. He became Vice-President and Chairman of the School for the Indigent Blind, Southwark; was appointed a member of the Royal Commission on the Blind and Deaf and Dumb; visited many Blind Institutions at home and abroad; and wrote a Report to Parliament on the Apparatus and Methods for the Instruction of the Blind, besides being on the Management Committee of several such institutions. He was Vice-President of the Congress for the Blind in Paris in 1878. He died at his residence, 4 Eaton Place, on January 3rd, 1895.