Clements Markham was the son of David Markham, vicar of Stillingfleet and canon of Windsor, and his wife, Catherine, daughter of Sir William Milner, 4th baronet, of Nun Appleton Hall, Yorkshire. He attended Cheam School and Westminster School. He joined the Royal Navy in 1844 but left in 1851. After his time on HMS Collingwood he had realised that he wanted to be an explorer and geographer.
"England and Wales, Marriage Registration Index, 1837-2005," index, FamilySearch (https://familysearch.org/pal:/MM9.1.1/2DQD-1H1 : accessed 15 Nov 2014), Clements Robert Markham, 1857; from Marriage, Barnstaple, Devon, England, , “England & Wales Marriages, 1837-2005,” findmypast.