It will remove the European Communities Act 1972 from the statute book and end the supremacy in Britain of EU law.
The government will also enshrine all existing EU law into British law and anything deemed unnecessary will be abolished later.
Her pledge comes as the Conservatives gather for their annual conference.
The repeal of the 1972 Act will not take effect until the UK leaves the EU under the process for quitting the bloc known as Article 50.
Mrs May has previously said she will not start the formal process of leaving the EU until next year.
