He was born in Nancy, France to Sir Henry John Cumming, a general in the British Army and received naval education at the Royal Naval College in Portsmouth. Cumming served as a midshipman in the Mediterranean and North America before being promoted to lieutenant in 1840 for his actions in the Syrian War. He remained with the Mediterranean Fleet until appointed to HMS "Frolic", a sloop stationed in South America. Whilst detached from "Frolic" and in command of a small pinnace on 6 September 1843 Cumming and seven men boarded a Portuguese slave ship, subdued her 27-man crew and brought her back to Rio de Janeiro. He had expected to be promoted for his efforts, but was overlooked and resented the decision for the rest of his life. Cumming spent some time in the Navy's Experimental Squadron before being promoted commander on 9 November 1846.