He was the elder of the two sons of General Andrew Cowell (d. 1821), originally of Coleshill, Buckinghamshire, and his wife Maria Justina (d. 1821), youngest daughter of Sir Thomas Stepney, 7th baronet of Prendergast, Pembrokeshire, and Llanelly House, Carmarthenshire.
[1] Cowell joined his father's regiment, the Coldstream Guards, and fought in the Peninsular War at Fuentes de Oñoro, Ciudad Rodrigo, Salamanca and Vittoria.
They had two sons, [James Charles] Murray Cowell (1824–54) and Sir [Emile Algernon] Arthur [Keppel] Cowell-Stepney, 2nd baronet (1834-1909).
A large memorial to him and the other Coldstream officers killed in the battle was erected in St Paul's Cathedral; a smaller version of it was placed in Llanelli parish church .
[8] This coincided with Cowell-Stepney attending the Basle Congress of the International Workingmen's Association in September 1869, where he was a delegate of the General Council.