Ernle was descended from John Ernle the Elder, Esquire, of Fosbury and Bishop's Cannings, Wiltshire, (born 1461/2), the ancestor of the Wiltshire branch of the family, and from John Ernle, Esq., of Sidlesham, Sussex (died 1465), whose wife Margaret was a daughter of Nicholas Morley, Esq., of Glynde Place, Sussex.