Whilst the House of Lords of the United Kingdom is the upper chamber of Parliament and has government ministers, it for many centuries had a judicial function. It functioned as a court of first instance for the trials of peers, for impeachments, and as a court of last resort in the United Kingdom and prior, the Kingdom of England.

Appeals were technically not to the House of Lords, but rather to the King-in-Parliament. In 1876, the Appellate Jurisdiction Act devolved the appellate functions of the House to an Appellate Committee, composed of Lords of Appeal in Ordinary (informally referred to as Law Lords). They were then appointed by the Lord Chancellor in the same manner as other judges.

During the 20th and early 21st century, the judicial functions were gradually removed. Its final trial of a peer was in 1935, and in 1948, the use of special courts for such trials was abolished. The procedure of impeachment became seen as obsolete. In 2009, the Supreme Court of the United Kingdom became the new court of final appeal in the UK, with the Law Lords becoming Supreme Court Justices.

The Supreme Court (initialism: UKSC or the acronym: SCOTUK) is the final court of appeal in the United Kingdom for all civil cases, as well as for criminal cases originating in England, Wales and Northern Ireland. It also hears cases of the greatest public or constitutional importance affecting the whole population.The Court usually sits in the Middlesex Guildhall in Westminster, though it can sit elsewhere and has, for example, sat in the Edinburgh City Chambers, the Royal Courts of Justice in Belfast, and the Tŷ Hywel Building in Cardiff.The United Kingdom has a doctrine of parliamentary sovereignty, so the Supreme Court is much more limited in its powers of judicial review than the constitutional or supreme courts of some other countries. It cannot overturn any primary legislation made by Parliament. However, as with any court in the UK, it can overturn secondary legislation if, for an example, that legislation is found to be ultra vires to the powers in primary legislation allowing it to be made.

Further, under section 4 of the Human Rights Act 1998, the Supreme Court, like some other courts in the United Kingdom, may make a declaration of incompatibility, indicating that it believes that the legislation subject to the declaration is incompatible with one of the rights in the European Convention on Human Rights. Such a declaration can apply to primary or secondary legislation. The legislation is not overturned by the declaration, and neither Parliament nor the government is required to agree with any such declaration. However, if they do accept a declaration, ministers can exercise powers under section 10 of the Human Rights Act to amend the legislation by statutory instrument to remove the incompatibility or ask Parliament to amend the legislation.

As authorised by the Constitutional Reform Act 2005, Part 3, Section 23(1), the Supreme Court of the United Kingdom was formally established on 1 October 2009 and is a non-ministerial government department of the Government of the United Kingdom. Section 23 of the Constitutional Reform Act limits the number of judges on the Court to 12, though it also allows for this rule to be amended, to further increase the number of judges, if a resolution is passed in both Houses of Parliament.It assumed the judicial functions of the House of Lords, which had been exercised by the Lords of Appeal in Ordinary (commonly called "Law Lords"), the 12 judges appointed as members of the House of Lords to carry out its judicial business as the Appellate Committee of the House of Lords. Its jurisdiction over devolution matters had previously been exercised by the Judicial Committee of the Privy Council.

The current President and Deputy President of the Supreme Court are Lord Reed of Allermuir and Lord Hodge respectively.