He first served as a midshipman on HMS Sybille in the Mediterranean (including an attack on Greek pirates), was promoted to lieutenant in 1830, before serving with HMS Ferret, until being promoted to commander on 21 September 1835.[2] He then served at that rank on HMS Castor off Spain's north coast during the Carlist War before receiving his first command, HMS Tweed, in the same theatre in 1837 and 1838, being awarded the cross of San Fernando for his services.[1][2] He rose to captain on 3 July 1840 and then commanded HMS Odin, a steam paddle frigate, in the Mediterranean Sea from 1847 to 1850.[2]
Initially Sir Maurice Berkeley declined to take Pelham on at the Board of Admiralty, in December 1856, due to his connections with Northumberland,[3] however Pelham joined the Board the following November as Fourth Naval Lord after Berkeley's retirement,[2] though left it four months later, in March 1858, having been promoted to rear admiral.[2] Under Dundas and the Duke of Somerset he joined the new Liberal board as Second Naval Lord in June 1859, remaining with it until resigning on grounds of ill health in early June 1861.[2]