	Rashleigh was the eldest surviving son of Jonathan Rashleigh MP, of Menabilly and his second wife Jane Carew, a daughter of Sir John Carew, 3rd Baronet of Antony, Torpoint, Cornwall. He succeeded to his father’s estates in 1702, when still a minor and was under the guardianship of his uncles. He was educated at Winchester College from 1704 to 1706 and matriculated at New College, Oxford on 4 September 1707, aged 18.