The Lord Privy Seal (or, more formally, the Lord Keeper of the Privy Seal) is the fifth of the Great Officers of State in the United Kingdom, ranking beneath the Lord President of the Council and above the Lord Great Chamberlain. Originally, its holder was responsible for the monarch's personal (privy) seal (as opposed to the Great Seal of the Realm, which is in the care of the Lord Chancellor) until the use of such a seal became obsolete. Though one of the oldest offices in European governments, it has no particular function today because the use of a privy seal has been obsolete for centuries; it may be regarded as a traditional sinecure, but today, the holder of the office is invariably given a seat in the Cabinet of the United Kingdom, and is sometimes referred to as a Minister without Portfolio.

Since the premiership of Clement Attlee, the position of Lord Privy Seal has frequently been combined with that of Leader of the House of Lords or Leader of the House of Commons. The office of Lord Privy Seal, unlike those of Leader of the Lords or Commons, is eligible for a ministerial salary under the Ministerial and other Salaries Act 1975. The office does not confer membership of the House of Lords, leading to Ernest Bevin's remark on holding this office that he was "neither a Lord, nor a Privy, nor a Seal".

During the reign of Edward I, prior to 1307, the Privy Seal was kept by the Controller of the Wardrobe. The Lord Privy Seal was the president of the Court of Requests during its existence.