The invocation of Article 50 by Prime Minister Theresa May marked a landmark shift for the United Kingdom as it officially began the process of leaving the European Union. This action followed the 2016 referendum in which 51.9% of voters opted for Brexit, indicating a clear desire among the electorate to sever ties with the EU. The article allows a member state to withdraw from the EU, and May's letter was directed to Donald Tusk, the President of the European Council, initiating a two-year negotiation period to determine the terms of the UK's exit and its future relationship with the remaining EU member states.

The invocation came during a time of political division across the UK, with considerable debate surrounding the implications of Brexit on trade, immigration, and social policies. In her letter, May outlined her vision for post-Brexit Britain, emphasizing the need for a global Britain that can forge its path while retaining strong ties with the EU in areas such as security and trade. The UK government's stance was to negotiate a new partnership based on mutual respect and shared values. This event was celebrated by numerous Brexit supporters who viewed it as a fulfillment of the referendum mandate.

The letter formally started the clock on a process that would lead to significant economic and political changes, not only for the UK but also for the EU. Negotiations were expected to cover various complex issues, including citizens' rights, the future of the Irish border, and financial settlements. As the exit discussions progressed, it became clear that differing views on the future relationship, especially concerning trade and customs arrangements, would define the years to come.