The PM's announcement on triggering Article 50 of the Lisbon Treaty - which begins the formal negotiation process - means the UK looks set to leave the EU by the summer of 2019.
Mrs May also promised a bill to remove the European Communities Act 1972 from the statute book.
She said this would make the UK an "independent, sovereign nation".
The repeal of the 1972 Act will not take effect until the UK leaves the EU under Article 50.