His proficiency in palaeographic knowledge persuaded Lord Langdale, who was Master of the Rolls in 1838 (the date of the Public Record Office Act), to offer him the post of Deputy Keeper (i.e. chief executive officer) at the new Record Office; force of ministerial pressure, however, compelled Lord Langdale ultimately to appoint Sir Francis Palgrave to the post. Hardy succeeded Palgrave as Deputy Keeper on 15 July 1861, and held the appointment to his death. As the head of his department he did much to render the records already in the custody of the Master of the Rolls accessible to the public, and muniments of three palatinates: Durham, Lancaster, and Cheshire were brought up to London and thrown open to inspection during his tenure. The appointment of the Historical Manuscripts Commission in 1869 was also largely due to his influence, and he was one of the first commissioners.