After Johnson resigned in 2022, Kwarteng supported Liz Truss's bid to become Conservative leader. Following Truss's appointment as Prime Minister, she appointed Kwarteng as Chancellor of the Exchequer. His appointment made him the first black person to serve as Chancellor of the Exchequer. On 23 September, Kwarteng announced various tax cuts in a "mini-budget" that was widely criticised and which briefly caused sterling to fall to its lowest-ever level against the US dollar. Kwarteng was dismissed as Chancellor on 14 October after 38 days, making him the second-shortest-serving post-war Chancellor.
Kwarteng was selected as the Conservative candidate for Spelthorne in January 2010. Kwarteng won the seat with a majority of 10,019 votes (21.2%). Kwarteng did not vote on the backbench EU Referendum Bill in October 2011. In 2013 he described the Help to Buy housing scheme as "inflationary".
In 2014, his book, War and Gold: A Five-Hundred-Year History of Empires, Adventures and Debt, was published. It is a history of capital and the enduring ability of money, when combined with speculation, to ruin societies. In 2015, his next book, Thatcher's Trial: Six Months That Defined a Leader, was published.
In March 2021, he was criticised for dissolving the Industrial Strategy Council, the advisory body seeking to regenerate Britain's regions. In the days after the COP26 climate summit, Kwarteng met oil industry bosses to encourage them to continue drilling in the North Sea.
In January 2022, while on a trip to Saudi Arabia, Kwarteng accepted flights and hospitality from Saudi Aramco, the majority state-owned energy firm. Kwarteng was also gifted a £300 Lenovo tablet. The BEIS department transparency data revealed that Kwarteng travelled to Saudi Arabia on a commercial flight costing the taxpayer £4,430. He also visited Aramco's Shaybah oil field with the Saudi energy minister, although this was not logged in BEIS transparency records. Opposition politicians criticised Kwarteng for accepting the Saudi state's hospitality, particularly in light of their human rights record, and raised concerns over whether he broke the ministerial code.
From August 2021, high European wholesale natural gas prices caused some smaller domestic suppliers in the United Kingdom to go out of business. In September 2021, the fuel supply crisis caused serious disruption to the supply of road fuel. Kwarteng said that "There is no question of the lights going out, of people being unable to heat their homes. There will be no three-day working week, or a throwback to the 1970s." He also said that the government would not rescue failed companies.Ed Miliband, Labour's shadow business secretary, accused Kwarteng of being complacent.
On 15 November 2021, Kwarteng published a letter of apology to Stone, in which he said he "did not mean to express doubt about your ability to discharge your role" and apologised for "any upset or distress my choice of words may have caused".
Chancellor of the Exchequer
Chancellorship of Kwasi Kwarteng 6 September 2022 – 14 October 2022
a Domestic energy support runs to Sep 2024, but only first 6 months is costed
Kwarteng was appointed Chancellor of the Exchequer by incoming Prime Minister Liz Truss on 6 September 2022. On 23 September 2022, he announced a set of economic policies named "The Growth Plan 2022" in what the Treasury described as a "fiscal event"; this was dubbed a "mini-budget" by the media. He refused to allow the Office for Budget Responsibility to assess the economic impact of the budget and provide a forecast.
Among the policies announced by Kwarteng was a cut in the basic rate of income tax from 20% to 19% to start in April 2023, the abolition of the 45% higher rate of income tax in England, Wales and Northern Ireland, the lifting of the stamp duty threshold, the freezing of energy bills, the reversal of the increase in National Insurance from April 2022, the abolition of the proposed Health and Social Care Levy, and the scrapping of the limit on bankers' bonuses. The Institute for Fiscal Studies director Paul Johnson called it "the biggest package of tax cuts in 50 years" and said that "the plan seems to be to borrow large sums at increasingly expensive rates, put government debt on an unsustainable rising path, and hope that we get better growth". The following week, sterling fell to its lowest-ever level against the US dollar, and turmoil in government bond prices led the Bank of England to launch an emergency bond buying programme. This caused house mortgage lenders to withdraw over 40% of their products, with other products repriced upwards. The International Monetary Fund cautioned that the measures would increase inequality.
Following criticism from several Conservative MPs, including Michael Gove, Kwarteng said on 3 October 2022 that the government would not pursue the plan to abolish the 45% higher rate of income tax paid by people earning over £150,000 a year. Kwarteng said the plan had become a "distraction from our overriding mission to tackle the challenges facing the country".
Kwarteng was dismissed as Chancellor on 14 October after only 38 days in post. This made him the second shortest-serving Chancellor after Iain Macleod, who died a month after taking office. Kwarteng was succeeded by Jeremy Hunt. Despite having already been dismissed as Chancellor, Kwarteng was appointed Second Lord of the Treasury on 18 October 2022.
Kwarteng's views on colonialism have been described by a PoliticsHome writer as "nuanced", stating that modern representation on historical events must be taken within historical context, "I think people should look at history with a bit more humility, and a little bit more critical inquiry. It’s very difficult not to have lots of preconceptions and lots of strongly held beliefs."
When asked about his thoughts on popular mob removal of British Empire-era statues and monuments, including that of slave trader Edward Colston, Kwarteng stated such removals were "acts of vandalism". In an interview, Kwarteng stated many supporters of the Black Lives Matter movement and critics of British imperialism have "a very kind of cartoon-like view" of the past, arguing for a greater understanding of the complexities of British history:
I think a lot of the debate around Black Lives Matter and imperialism or colonialism has a very kind of cartoon-like view of what was happening over centuries across a quarter of the world.
Reactions to his stances on racial and colonialism issues have ranged from support to opposition. On 26 September 2022, Labour Party MP Rupa Huq was suspended after calling Kwarteng "superficially black" in response to his comments. On 27 September, racial correspondent Nadine White wrote in support of Kwarteng, criticizing "performative allyship" in UK culture, adding that disingenuous "faux outrage" towards Huq's comments just veiled ingrained racism within politics.
Author Nels Abby, writing for the Guardian, states Kwarteng did not help Black British citizens looking for representation, "as a chancellor he was a dud, but as a diversity role model, he was even worse".
In August 2012, Kwarteng co-authored a book with four fellow MPs, titled Britannia Unchained. The book argues for a radical shrinking of the welfare state in order "to return it to the contributory principle envisioned by its founder Sir William Beveridge – that you get benefits in return for contributions".
Kwarteng is described by friends as an "intensely private" person. He was previously in a relationship with former Conservative Home Secretary Amber Rudd. He married the City solicitor Harriet Edwards in December 2019. Their daughter was born in 2021. He has lived in Bayswater, and in January 2022 purchased a house in Greenwich. He is a member of the Garrick Club.