Three and a half years after the United Kingdom voted to leave the European Union, the United Kingdom is set to withdraw formally on January 31, 2020, at 11 p.m. (U.K. time). On January 24, the Withdrawal Agreement was signed by Boris Johnson, Prime Minister of the UK, Ursula von der Leyen, President of the European Commission, and Charles Michel, President of the European Council. The European Parliament subsequently voted to approve the Agreement on January 29th. Prior to the signing of the Withdrawal Agreement, the European Union (Withdrawal Agreement) Act received Royal Assent on January 23, 2020. The Act will implement the Withdrawal Agreement in the United Kingdom.

The United Kingdom is the first EU member state with withdraw from the Union of which it was a member since 1973. Prior to the entry into force of the Treaty of Lisbon in 2009, there had been no formal mechanism for state withdrawal in the EU Treaties. However, the introduction of Article 50 of the Treaty on European Union permitted the member states "to withdraw from the Union in accordance with [their] own constitutional requirements." Once the UK formally withdraws on the 31st, negotiations between the UK and the EU as to the details of their future relationship will begin.