Wednesday’s result came on the day the divisive, unrepentant leader ended his final appearance in Parliament as prime minister with the words “hasta la vista, baby”.
The pair came first and second in a vote of Conservative lawmakers on Wednesday. Trade Minister Penny Mordaunt came in third and was eliminated.
The race pits Sunak, who steered Britain’s economy through the pandemic, against Truss, who has led the UK’s response to Russia’s invasion of Ukraine.
The two contenders will spend the next few weeks campaigning for the votes of about 180,000 Conservative Party members around the country, who will vote by postal or online ballot.
The winner of the party leadership vote will be announced on September 5 and will automatically become Britain’s next prime minister.
Sunak won every round of voting by lawmakers but is less popular with the party’s grassroots. Truss is a favourite of the party’s right wing.
The bitter campaign has exposed deep divisions in the Conservative Party at the end of Johnson’s scandal-tarnished three-year reign.
Truss has branded Sunak a “socialist” for raising taxes in response to the economic damage wrought by the coronavirus pandemic and the war in Ukraine.
Sunak has hit back, saying that his rivals are peddling economic “fairy tales” to British voters as the country faces high inflation.
All the contenders — there were 11 to start — sought to distance themselves from Johnson, whose term in office began boldly in 2019 with a vow to “get Brexit done” and a resounding election victory, but is now ending in disgrace.
On Wednesday, he faced derisive opposition politicians and weary Conservatives at his last Prime Minister’s Questions session in the House of Commons.
It was a downbeat departure, with supportive Conservative backbenchers lobbing praise and opposition politicians offering variations on “good riddance”.
Johnson extolled what he called his accomplishments — leading Britain out of the European Union and through COVID-19, and supporting Ukraine against Russia’s invasion.
“Mission largely accomplished, for now,” he said, before departing with Arnold Schwarzenegger’s “hasta la vista” catchphrase from Terminator 2.
Opposition Labour Party leader Keir Starmer said he would “miss the delusion”.
He finally quit after one scandal too many — appointing a politician accused of sexual misconduct — drove his ministers to resign en masse.
Despite remaining prime minister, he has largely disappeared from the scene, even as Britain faces a summer cost-of-living crisis and labor discontent as inflation hits 9.4 per cent.
Last week he took a ride in a Royal Air Force Typhoon fighter jet, with “Top Gun”-style footage released by his office, then threw a weekend party at Chequers, the country house that comes with the prime minister’s job.
London Mayor Sadiq Khan accused Johnson of wanting to “become Tom Cruise” and urged him to resign immediately.
“We need a full-time prime minister looking after our country rather than somebody who’s checked out,” Khan said.