Born in Exeter, Devon, and called Charles Cornwallis Michell later in his life because of the proximity to Cornwall of his birthplace, Michell was educated at the Royal Military Academy, Woolwich and commissioned into the Royal Artillery in 1809. He headed a brigade at the battles of Vittoria and Toulouse, took part in Waterloo and was appointed teacher of military drawing at the Royal Military College, Sandhurst on 24 March 1824 and professor of military fortification at Woolwich on 25 December 1825 and promoted to the brevet rank of major shortly thereafter. He was fluent in Spanish, Portuguese and French.