PA
This means that Parliament will have the opportunity to either approve or turn down the deal that May and EU leaders establish at the end of the two-year negotiating process initiated by the triggering of Article 50.
Crucially, this is not the issue that was put before the Supreme Court before Christmas. Judges will rule later this month whether May is required to secure parliamentary approval before she invokes Article 50 - not after it.
Here's the key extract from the prime minister's speech:
"And when it comes to Parliament, there is one other way in which I would like to provide certainty. 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."
On the surface, May's comments may feel like a victory for parliamentary sovereignty and specifically Remain and soft Brexit MPs who are troubled by the prime minister's intention to terminate Britain's single market membership. Today the news appeared to cause Sterling to rally slightly as investors saw a possible route out of a hard Brexit.
However, in reality, it's nothing more than a gesture - and a very clever one.
The prime minister has left parliamentarians between an unaccommodating rock and an extremely hard place. Soon after May's speech in Westminster on Tuesday morning, Brexit minister David Davis confirmed that Britain would leave the 28-nation bloc at the end of the Article 50 process, whether an exit deal is in place or not.
This means that as soon as the Article 50 period reaches its conclusion, Parliament will be presented with two clear choices: either 1) approve the deal May has negotiated, or 2) rebuff it and let Britain crash out of the EU without an exit deal in place.
For Remainers - like former Labour leadership candidate Owen Smith and Liberal Democrat leader Tim Farron to name but a few - this is not a desirable scenario. It would be a choice between two evils, with one being even more unpalatable than the other. Most Remain MPs would conclude that they had little choice but to back May's deal, no matter how many problems they have with what's on offer. To do otherwise would, in all likelihood, boot Britain into an even harder version of Brexit than the one May finally puts on the table.
Theresa May's pledge to hold a vote on Brexit hasn't handed the pro-Remain camp a lifeline - it's handed them a noose.