The former chancellor topped every ballot with Tory MPs - and won 137 votes in the final run-off compared to 113 for Ms Truss.
However, the bookies’ have placed the Foreign Secretary as the favourite among party members, meaning it is all still to play for.
But what do Mr Sunak and Ms Truss stand for and what have they promised to do if they become the prime minister?
Here’s what you need to know.
Brexit - Truss
Ms Truss voted to remain in the EU and campaigned for Remain in the lead-up to the referendum.
However, she has managed to position herself as the favourite Brexit contender in the leadership contest, gaining the support of staunch Brexiteers such as Jacob Rees-Mogg and Nadine Dorries.
She recently told The Telegraph: “If I could go back to 2016, I would vote to leave.
“What I’ve seen in both my job in trade and my role as Foreign Secretary is the new freedom and impetus that having an independent trade policy and independent foreign policy has enabled us to do.”
In her leadership announcement, she said she would work to expand the “vast opportunities” that Brexit has brought the UK.
Brexit - Sunak
Mr Sunak on the other hand has always been a Brexiteer - and publicly supported the Leave campaign ahead of the referendum.
He sold Brexit as a "once in a generation opportunity" to "take back control” and said the vote would result in a "freer, fairer and more prosperous" Britain.
His Parliamentary voting record shows an enduring belief in a separation from the EU.
He has historically voted against greater integration with the EU and was among the Tories supporting a no-deal exit.
Tax - Truss
The headline policy of Ms Truss’ leadership pitch is to cut taxes immediately if she assumes the role of Prime Minister.
She has promised £30 billion in tax cuts and has said she would reverse both the National Insurance hike, put in place by Mr Sunak, as well as next year’s corporation tax hike - stating she will “keep corporation tax competitive”.
According to TheyWorkForYou, the Foreign Secretary voted for a ‘mixture of for and against’ measures to prevent tax avoidance, as well as a ‘mixture of for and against’ higher taxes on banks.
Tax - Sunak
Mr Sunak has positioned himself as a fiscally conservative candidate, slamming his opponents who have pledged to cut taxes as telling “comforting fairy tales”.
He said he will only implement tax cuts once the country has a grip on inflation.
The National Insurance increase will remain in place if the former chancellor becomes prime minister, and he plans to raise corporation tax from 19% to 25% from 2023.
He added that business tax cuts will be prioritised, previously pledging a 1p income tax cut in 2024.
He ‘consistently’ voted against higher taxes on banks and ‘consistently’ voted for raising the threshold at which people start to pay income tax.
Environment and Net Zero - Truss
Ms Truss has said she wants to maintain the UK’s 2050 net zero target, but wants to reconsider some net zero policies.
She told The Spectator: “I’d have a temporary moratorium on the green energy levy to enable businesses and industry to thrive while looking at the best way of delivering net zero.”
In her former role as Environment Secretary from 2014 to 2016, Ms Truss cut subsidies for solar farms, criticising solar power on agricultural land as harmful to food security.
She also has ties to the oil industry, as a former commercial manager at Shell, and publicly supported the expansion to Heathrow Airport.
Ahead of COP26 last year, Ms Truss said: “The way to reduce climate emissions from flying isn’t to stop flying, it is to create the new generation of next technology.”
Her voting record says she ‘generally’ voted against action to prevent climate change.
Environment and Net Zero - Sunak
Mr Sunak has promised to adhere to the Conservative Party’s manifesto pledge to reduce the UK’s carbon emissions to net zero by 2050.
As chancellor, in February, Mr Sunak pushed to fast-track the approval of six oil and gas fields.
In April, he blocked the Department of Business, Energy and Industrial Strategy’s proposals for home insulation.
Contrastingly, Mr Sunak did, however, promote measures to force banks and other companies to account for their greenhouse gases.
According to TheyWorkForYou, Mr Sunak has ‘almost always’ voted against measures to prevent climate change.
Immigration - Truss
Ms Truss has ‘consistently’ voted for stronger enforcement of immigration rules, as well as stricter rules on asylum.
She told The Times she will try to expand the Rwanda migrant removal scheme to countries such as Turkey if she becomes prime minister.
The Foreign Secretary has reportedly told MPs in private that she would like to emulate the deal struck with Rwanda in an effort to combat the Channel migrant crisis.
Immigration - Sunak
Mr Sunak has also voiced support of the Rwanda deportation policy, saying it will prove vital in stopping criminal gangs from endangering vulnerable migrants.
He told BBC Radio 4: “This country has a proud history of welcoming people but it’s also vital that we’re in control of who’s coming here.”
A spokesperson said he was proud to come from a family of immigrants but he believed the UK must control its borders.
He ‘almost always’ voted for a stricter asylum system.
LGBTQ+ Rights - Truss
Ms Truss has consistently voted in favour of same sex marriage and equality for gay rights.
In the past, she has been criticised by LGBTQ+ groups for saying she agrees with Labour MP Rosie Duffield that “only women have a cervix”.
She said at the Conservative Party Conference in 2021: “I think we’ve taken the right approach with transgender people. We’ve made the process simpler [and] we’ve made the process kinder.
“I have full respect for transgender people, however it wouldn’t be right to have self-identification with no checks and balances in the system - those medical checks are important.”
LGBTQ+ Rights - Sunak
Mr Sunak has never voted on gay rights, and in 2019, he was absent on a vote about extending same-sex marriage to Northern Ireland.
The Daily Mail reports he is set to lay out a “manifesto for women’s rights” in which he will argue that transgender women should be excluded from women’s sporting events, and call on schools to “be more careful” in teaching on “issues of sex and gender”.
Defence - Truss
Ms Truss said as prime minister she would want defence spending to be 3% of GDP by the end of the decade - above the current Nato target of 2%.
Her target would involve spending tens of billions of pounds more on bolstering the UK’s defensive capabilities, which she said was justified given Russia’s invasion of Ukraine.
The Foreign Secretary has previously voted to replace Trident with a new nuclear weapons system.
Defence - Sunak
Mr Sunak announced generous spending commitments in support of Ukraine following Russia’s invasion.
More than £2.3 billion has been given to Ukraine in the form of military support.
If he becomes prime minister, he has vowed to prioritise funding for the armed services and has committed to maintain defence spending levels.
Health and Social Care - Truss
Ms Truss has ‘almost always’ voted to reduce spending on welfare benefits, as well as housing benefits.
She also voted against increased benefits for those with long-term illnesses or disabilities.
Health and Social Care - Sunak
Mr Sunak also voted against increased benefits for those with long-term illnesses or disabilities, and voted for a reduction in spending on welfare benefits.
As chancellor, he introduced the hike in National Insurance contributions to fund increased health and social care spending.
Previously, he announced £6 billion of investment to tackle NHS waiting lists in England and improving the use of digital technology in hospitals.
Mr Sunak also doubled NHS efficiency targets to 2.2 per cent a year, freeing up £4.75 billion to fund NHS priority areas over the next three years.
But he frequently came under pressure to do more to help the NHS operate.