Should May see off any challenge, the next step might prove tougher. The prime minister has promised a meaningful vote on the draft text in Parliament in December. That means she would need a simple majority of the 650 lawmakers that sit in the House of Commons.
Those numbers look unlikely.
Her 315 Conservative MPs do represent the largest party in the House, but a significant number are against the plan. The Conservatives operate a majority in the Commons by working in tandem with 10 votes from the Democratic Unionist Party (DUP). The DUP, a Northern Irish party, have expressed concern that May's deal treats that part of the United Kingdom differently — something of a red line for the hard-line unionists.
The left-of-center opposition Labour Party has 257 lawmakers and would appear to hold the whip-hand. Labour has indicated they will ask their MPs to vote against May's deal, but there are a number of rebels that May can count on. It's estimated she would need around 40 Labour MPs to cross the divide and vote for her. Despite deep divisions within Labour, political analysts see that as a high threshold.
The third-biggest party, the Scottish National Party (SNP), has promised that all 35 of its MPS will reject the deal, calling it an unfair solution for Scotland.
A rejection by Parliament would likely spell the end of May's tenure, according to many onlookers, and could lead to another General Election or even a second Brexit referendum.