The Law Adviser to the Lord Lieutenant of Ireland was an official of the English Crown in nineteenth-century Ireland.
The office was created in 1831 to ease the heavy workload of the existing Irish Law Officers, the Attorney General for Ireland and the Solicitor General for Ireland.
No specific duties were assigned to the Law Adviser when the office was created: he appears at first to have been simply a general assistant to the senior Law Officers. Later he was given the tasks of drafting Parliamentary Bills, and of advising lay magistrates on any legal problems which they referred to him. Cases involving State security also fell under his remit: Denis Caulfield Heron in 1867 was heavily occupied in prosecuting the trials which followed the Fenian Rising.
At first the Law Adviser was usually a Serjeant-at-law, but in time the position was open to rising barristers who hoped in due course to be appointed to the Bench; later it seems to have been felt that the offices of Serjeant and Law Adviser should be separate. There may have been a feeling that some of the work of the Law Adviser was beneath the dignity of the ancient office of Serjeant. The Attorney General generally had the final word in the appointment: certainly this was so in 1841 when Francis Blackburne insisted on the appointment of Abraham Brewster, despite strong opposition from Daniel O'Connell, who disliked Brewster.
The Law Adviser's duty to advise magistrates on points of law was open to criticism as an interference by the Crown with the independence of the judiciary. In particular John Naish, the last nineteenth-century Law Adviser, was attacked by political opponents for openly assisting magistrates in their ongoing struggle with the Irish National Land League. He was also criticised for suggesting that they rely on an obscure medieval statute, 34 Edward III c.1, to imprison those who could not find surety for their good behaviour. Since the statute had clearly been intended only to deal with cases of riot, this was arguably a deliberate misreading of the law. Perhaps because of this controversy the office was left vacant after Naish's promotion to the office of Solicitor General in 1883. It was briefly revived in 1919, but finally abolished by the Irish Free State in 1924.