For more on when May could trigger exit talks, see: The government suffered two heavy defeats in parliament during the legislative process, inserting conditions into the bill saying May must guarantee the rights of European Union nationals living in Britain and give lawmakers more powers to reject the final terms she reaches with the EU.
This means the EU (Notification of Withdrawal) Bill passed the House of Commons without any changes and would now go back to the Lords, where it is expected to be passed.
Brexit Secretary David Davis insisted in interviews on Sunday that the government is working on a contingency plan in the event of talks with Brussels stalling.
Both houses backed the "Brexit bill" and after securing symbolic approval from Queen Elizabeth, expected in the coming days, May has the right to begin what could be Britain's most complex negotiations since World War ll.
With all the legal hurdles out of the way, PM May is free to trigger Article 50.
Meantime, Scotland should hold another independence referendum between autumn 2018 and spring 2019, first minister Nicola Sturgeon said on Monday, and she will begin the process to hold the poll next week.
The House of Lords last week attached two amendments to the bill, created to give parliament a veto on the terms of Britain's withdrawal and to reassure European citizens that they will get a guaranteed right to stay in the United Kingdom after Brexit.
If Britain fails to secure a deal with the European Union within two years, Britain will still leave the European Union but the precise terms of its exit deal might be decided by the courts.
But she can't do it until Parliament approves a bill authorizing the government to start the divorce process.
Baker also praised Parliament's efforts to keep negotiations simple.
"The simple truth is we have been planning for the contingency - all the various outcomes, all the possible outcomes of the negotiations", Davis said.
After Britain voted to leave the EU, we look at which European countries want to hold their own EU referendum.
Labour Leader Jeremy Corbyn accused May's government of being "complacent", warning the prime minister that "if the wrong decisions are made, we'll pay the price for decades to come".
Should the bill pass tonight, May will have the rest of the month to decide when to trigger Article 50.
With a vote set for Monday on a bill granting May the authority to open divorce talks with the European Union, some Conservative lawmakers are pushing for Parliament to have a say on what happens if negotiations break down without an agreement.
He also criticised Labour, saying they "sat on their hands" when they could have been blocking May's hard Brexit.
Speaking in Edinburgh, Sturgeon said it was clear the United Kingdom was heading for a "bad deal" on Brexit.