Blandford is the eldest son of the 11th Duke of Marlborough, and his first wife, Susan Mary Hornby (later Mrs John Gough).
He was largely disowned by his father, who disapproved of his lifestyle, in 1994. Although he will inherit the title of Duke of Marlborough upon his father's death, the ownership of the estate (including Blenheim Palace) and chairmanship of its managing trust will pass to Blandford's son George Spencer-Churchill, Earl of Sunderland.
Spencer-Churchill spent a month in prison in 1995 for forging prescriptions. In September 2007 he was jailed for six months for two counts of dangerous driving and one charge of criminal damage following a 'road rage' attack on another motorist's car. At the same time he also received a three and a half year driving ban.