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.