May said there would have to compromises in the negotiations but it was important to provide "as much certainty as possible" and there would be proper scrutiny.
"When it comes to parliament, there is one other way I would like to provide certainty," she said in a speech in London.
"I can confirm today that the government will put the final deal that is agreed between the UK and the EU to a vote in both houses of parliament before it comes into force."
She said that Britain would not seek a deal that left the country "half in, half out" of the European Union when it negotiates its exit from the bloc.
"We see a new and equal partnership between an independent, self-governing, global Britain and our friends and allies in the EU. Not partial membership of the European Union, associate membership of the European Union or anything that leaves us half in, half out," May said in a speech.
"We do not seek to adopt a model already enjoyed by other countries. We do not seek to hold on to bits of membership as we leave. No - the United Kingdom is leaving the European Union and my job is to get the right deal for Britain." May also said she wanted the bloc to remain successful. "It remains overwhelmingly and compellingly in Britain's best national interest that the EU should succeed," she said.