De la Beche was born in Welbeck Street, Cavendish Square, London. He was the only son of Thomas De la Beche (1755–1801) and his wife, Elizabeth. The family name was originally Beach, but his father changed it to create a fictional connection with the medieval Barons De la Beche of Aldworth, Berkshire. His father served as a brevet major (later lieutenant-colonel) in the Norfolk fencible cavalry regimentan officer in the British Army, and was a slave owner with an estate in Jamaica. In 1800 the family travelled to the plantation in Jamaica when Thomas inherited the estate and his father died there in the following year. Mother and son returned to England, having been shipwrecked to the north of San Domingo on their journey.