Former British foreign secretary Boris Johnson and current foreign secretary Jeremy Hunt are the final two in the race to replace Prime Minister Theresa May.
A fifth and final ballot of Conservative Party lawmakers has eliminated Environment Secretary Michael Gove.
Johnson was again way out in front, winning 160 out of 313 votes against Hunt's 77. One ballot paper was rejected.
Johnson, 55, who served as London mayor for eight years, has cast himself as the only candidate who can deliver Brexit on October 31 while fighting off the electoral threats of Nigel Farage's Brexit Party and Jeremy Corbyn's Labour Party.
Johnson has increased his share of the vote of Conservative lawmakers at each of the four ballots so far: 114 out of 313 votes in the first ballot on June 13, 126 on June 18, 143 on Wednesday, and 157 and 160 on Thursday.
Gove was third with 75. Interior minister Sajid Javid was knocked out in the fourth round earlier on Thursday.
Now around 160,000 Conservative Party grassroots members will vote on who will be their leader - and Britain's next prime minister - by the end of July.
Johnson has pledged to leave the EU on October 31 with or without a deal. The EU has said it will not renegotiate the divorce deal that May agreed last year and the British parliament has indicated it will block a no-deal exit.
He has not addressed how he will solve that riddle.
Australian Associated Press