May, who lacks the confidence of large parts of the Conservative party after two years of bumbling Brexit negotiations and has few allies left, made the announcement as a last-ditch incentive to persuade her wayward lawmakers to back her deal ahead of a possible third vote on it.
No exact date for the resignation was offered by the prime minister, but a leadership election would be expected before the start of the summer after Britain leaves the EU. That would keep the deeply unpopular May away from the second phase of Brexit negotiations in which Britain will agree what its future trading relationship with the EU will look like.
The prime minister hopes that by sacrificing herself she'll push more of her lawmakers to back the deal in a possible third vote by the end of the weekand in doing so secure her legacy as the leader who followed the instructions of the British electorate and took Britain out of the EU.
She told a meeting of Conservative lawmakers Wednesday afternoon: I am prepared to leave this job earlier than I intended in order to do what is right for our country and our party. The prime minister said she knew members of parliament didn't want her to lead the next phase of Brexit negotiations, and added: I won't stand in the way of that.
However, if it's rejected againand the parliamentary arithmetic is still not on her sidethe deadline with no deal is 12 April. May runs a minority government and will require the support of the Northern Irish Democratic Unionist party in order to get her deal through. They have announced that they still can't back the deal despite May's new promise.
If the deal is agreed, the fresh deadline for Britain leaving the EU would be 22 May. A Conservative party leadership election would take place shortly afterwards. Pro-Brexit lawmakers who didn't back the deal before might now take the plunge in the hope of installing one of their own as the new leader.
May's arch leadership rival, Boris Johnson, was reportedly smiling from ear to ear as he left prime minster's meeting Wednesday. Previously one of the deal's biggest and most vocal critics, he shamelessly announced that he would now be backing it following May's promise to resign.
In another possible roadblock, the speaker of the House of Commons has indicated that May might not even be allowed to call a third vote on the deal. John Bercow ruled last week, citing an obscure precedent set in the year 1604, that May is not permitted to call a vote on something that is substantially the same as a proposal that has already been rejected by the House.
If May's deal is rejected againor if it's blocked from a votethe way forward on Brexit is entirely unclear. In a separate development Wednesday, lawmakers voted on eight different alternatives including a second referendum, canceling Brexit, and staying inside a customs union with the EU. Every single proposal was rejected by members of parliament.
May's deal has been resoundingly rejected by the British parliament twiceonce in January with the largest ever defeat in the House of Commons, and again earlier this month by a slightly smaller margin.
Today she tried to make a decisive move to change her fortunes. But, in truth, the way out of the Brexit mess is no clearer than it was.