Britain's governing Conservatives are set to pick two candidates who will square off to become the country's next prime minister.

Lawmakers will vote Thursday to eliminate two contenders from a four-strong field of ex-foreign minister Boris Johnson, current Foreign Secretary Jeremy Hunt, Environment Secretary Michael Gove and Home Secretary Sajid Javid.

Johnson has a commanding lead after three rounds of voting that cut the list from an initial 10 contenders. The three others are battling to join him in a runoff to be decided by 160,000 Conservative Party members nationwide.

British Conservative party leadership and prime minister contender Boris Johnson leaves home in South London in London, Thursday, June 20, 2019. The race to become Britain's next prime minister is down to the final four on Wednesday, as Johnson stretched his lead among Conservative lawmakers and upstart Rory Stewart was eliminated from the contest. (AP PhotoMatt Dunham)

British Conservative party leadership and prime minister contender Boris Johnson leaves home in South London in London, Thursday, June 20, 2019. The race to become Britain's next prime minister is down to the final four on Wednesday, as Johnson stretched his lead among Conservative lawmakers and upstart Rory Stewart was eliminated from the contest. (AP PhotoMatt Dunham)

All the candidates are vowing to lead Britain out of the European Union, a challenge that defeated Prime Minister Theresa May. She quit as Conservative leader earlier this month after failing to win Parliament's backing for her Brexit deal.

British Conservative party leadership and prime minister contender Boris Johnson leaves his home in south London, Thursday June 20, 2019. The race to become Britain's next prime minister is down to the final four on Wednesday, as Boris Johnson stretched his lead among Conservative lawmakers and upstart Rory Stewart was eliminated from the contest. (AP PhotoMatt Dunham)

British Conservative party leadership and prime minister contender Boris Johnson leaves his home in south London, Thursday June 20, 2019. The race to become Britain's next prime minister is down to the final four on Wednesday, as Boris Johnson stretched his lead among Conservative lawmakers and upstart Rory Stewart was eliminated from the contest. (AP PhotoMatt Dunham)