On Tuesday night, the Prime Minister signed the letter saying the UK was leaving, and on Wednesday at 12.30pm it will be handed to European Council President Donald Tusk in Brussels by Sir Tim Barrow, the British ambassador to the EU.
It is only at that point that Article 50 is triggered, firing the starting gun on two years of negotiations to extract the UK from the bloc.
The talks will include how much money Britain owes for bailing out and what trade deal - if any - can be hammered out once the UK quits the single market, the Huffington Post reported.
May will on Wednesday make a statement to Parliament where she will set out to MPs her determination to build a Britain with a “truly global outlook”.
Earlier in the evening, May spoke to German Chancellor Angela Merkel, the President of the European Council, Donald Tusk, and the President of the European Commission, Jean-Claude Juncker, all key players in the talks ahead.
Britain was stunned during the referendum last June, when 51.9 percent voted Out. If the timing runs to schedule, by the end of March 2019 the UK will become the first state to leave the union in its 60-year history.