Truss had been locked in a five-week leadership battle with former chancellor Rishi Sunak for the keys to Number 10 Downing Street.
The South West Norfolk MP won with 81,326 votes to Sunak's 60,399, according to the result announced today (5 September) at a Westminster gathering by 1922 Committee Chair Sir Graham Brady.
She was widely predicted to win the leadership competition by bookmakers, and following her win, Truss addressed the crowd, calling her election a "honour" and thanking those who had "faith" in her.
But who is Liz Truss?
Here is everything you need to know about her.
Who is Liz Truss?
Brought up in Yorkshire, the married mother-of-two, whose relationship survived an affair with former Tory MP Mark Field before her election to the Commons, boasts an impressive CV.
Defying her upbringing by left-leaning parents, Truss has held posts such as education minister, environment secretary and justice secretary in previous Conservative governments.
Elected to Parliament in 2010, she previously worked in the energy and telecommunications industry and is a qualified management accountant.
From being mocked for her outrage about cheese imports to being appointed to one of the great offices of state, Truss has made a steady rise up the Cabinet ladder.
She has been rewarded after being seen to have made a success of her international trade secretary post.
Truss underwent a transformation from being pro-Remain to an avid Brexiteer following the referendum in 2016.
While the Government faced tough headlines about deadlock in the negotiations with the European Union during the Brexit transition period, the South West Norfolk MP made a host of trade deals for the UK, ensuring the terms agreed while an EU member were ready to continue after exiting the bloc.
A coveted trade deal with the US eluded her, but Truss won plaudits in the Conservative Party for securing new terms with Japan and Australia, while a New Zealand agreement is said to be nearing completion.
Her Labour critics, however, bemoan that she did not deliver a “single trade deal that we didn’t already have inside the EU”, calling the praise within Government for her performance overblown.
Where was she educated?
Truss studied philosophy, politics and economics at Merton College, Oxford, where she became president of the University Liberal Democrats.
Almost half of Johnson’s new Cabinet went to Oxford or Cambridge universities and 60% attended a private school, a social mobility charity has said.
The percentage privately educated is down slightly on the Prime Minister’s previous cabinets, data from the Sutton Trust suggested.
New Foreign Secretary Truss, Housing Secretary Michael Gove and Chancellor Rishi Sunak all attended Oxford University.
The trust said just over a quarter of Cabinet ministers attended both independent schools and Oxbridge.
What has she said about cheese?
Away from politics, Truss’s flair for social media has seen her offer an insight into her private life by updating her Instagram account with pictures of her relaxing at the beach, or behind the scenes at official events.
Infamously, the worlds of social media and politics combined in 2014, when her improbably enthusiastic speech about opening pork markets in Beijing went viral, pilloried on satirical programmes such as Have I Got News For You?
She caused further hilarity when telling the Tory Party conference that year: “We import two-thirds of our cheese, that is a disgrace.”