Clarke was born at Olney, Buckinghamshire; his father and grandfather were prosperous lace merchants.
Here he managed to get the run of Thomas Cadell the younger's library in the Strand, and became acquainted with literature and literary people.
For a time he acted as Dermott's amanuensis, and afterwards aided Michael Ryan in the London Medical and Surgical Journal.
[1] For 30 years Clarke was on the Lancet, and at the same time carried on a medical practice in Gerrard Street;[1] he became a licentiate of the Society of Apothecaries in 1837, and a member of the Royal College of Surgeons in 1852.
[1] On ceasing to write for The Lancet, published his reminiscences in the Medical Times and Gazette.