British prime minister runoff down to May and Leadsom

May (right) won 199 votes out of the party's 329 MPs and Leadsom secured 84 votes, while Justice Minister Michael Gove was knocked out of the contest after coming in third place with 46 votes.

Some 150,000 Conservative Party members will now vote between the two women, with the results of who will become the new prime minister to be announced on September 9.

The winner will replace David Cameron, who announced he would step down following last month's referendum for the UK vote to leave the European Union.

The next prime minister will be tasked with the complicated process of negotiating the UK's departure from the 28-member bloc.

A veteran politician, May has vowed to negotiate the UK's departure from the EU despite her support for the Remain campaign.

"We need proven leadership to negotiate the best deals for leaving the European Union," May said outside the parliament after the announcement on Thursday. "This vote shows that the Conservative Party can come together and under my leadership it will," she said.

Leadsom, a relative political novice who entered parliament in 2010, campaigned for the Leave campaign. She has vowed to secure trade details with the EU while also controlling immigration.

Those goals clash with the EU's position that the UK cannot pick and choose what parts of the EU it likes and doesn't like when it departs.

The early September date for the leadership results to be announced cast a cloud of uncertainty over the next two months as to how the island will move forward with its departure.

That uncertainly is likely to further roil markets, which have already been hit by the shock of the referendum vote. EU leaders have urged Britain to make a swift decision to trigger Article 50, which will then set in motion a two-year process to leave the EU.

cw/kms (AP, AFP, Reuters)