 Sanderson was born at Gunton Park, about six miles north of Aylsham, Norfolk, the second son of Richard Sanderson, Member of Parliament for Colchester from 1832 to 1847, and the Honourable Charlotte Matilda Sanderson Manners-Sutton, elder daughter of Charles Manners-Sutton, Speaker of the House of Commons from 1817 to 1835.He was educated at Eton until he was forced to leave the school in 1857 due to the poor state of his family's finances, caused by the death of his father in October of that year, and his father's business in East India failing.Sanderson entered the Foreign Office as a junior clerk in 1859 and was not to leave the Foreign Office until his retirement in 1906.