Smith was born in Ashford, Kent; her family moved to Norfolk when she was three years old. Growing up in Stoke Ferry, she attended comprehensive schools in Swaffham and Methwold; after a gap year working for former Conservative Education Secretary Gillian Shephard, she read English Literature at the University of York. She undertook summer work for Bernard Jenkin. After graduating from York University, she joined Deloitte Touche Tohmatsu as a management consultant. She advised private businesses, government departments and public bodies. In 2007, Smith was chosen to be the Conservative Party candidate for the constituency of Norwich North at the general election. She then took leave from her job, working for Conservative Central Office on secondment, to "draw up detailed plans to put our policies into practice".
Parliamentary career
Following the resignation of Labour MP Ian Gibson, Smith became the Conservatives' by-election candidate and subsequently gained the seat, becoming the youngest member of the House of Commons. She took her seat in the House of Commons when the parliamentary break ended in October. On 14 October 2011, she was appointed Economic Secretary to the Treasury in a ministerial reshuffle, becoming the youngest minister serving in government at that point. According to The Guardian newspaper Smith was appointed to the role because David Cameron wrongly believed she was a trained accountant. On 26 June 2012, she appeared on the BBC Two current affairs programme Newsnight and was interviewed about Chancellor George Osborne's decision that day to delay plans to increase fuel duty. Interviewer Jeremy Paxman questioned the apparent change in her views on fuel duty. The interview attracted much comment from the media and other political figures, and was described as a "mauling" and a "humiliation" for Smith. Politicians, including John Prescott and Nadine Dorries, questioned Osborne's judgement for sending a junior minister onto the programme in his place. In August 2013, she was criticised by transparency campaigners for blocking the identification of civil servants and public sector bodies responsible for £77m of flights booked through the Government Procurement Service. In October 2013, she resigned from the Cabinet Office to "concentrate on the most important part of my job: being the Member of Parliament for Norwich North". During the campaign for the 2015 general election, Smith was mocked by political opponents for quoting a constituent's letter in her election literature. The letter, first published in the Norwich Evening News newspaper, said she seemed "to act more like a Socialist than a Conservative". Political Scrapbook, the left-wing political blog, published a mocked-up photograph depicting Smith as Marxist "urban guerilla" Wolfie Smith giving a clenched fist salute outside Norwich railway station. Smith responded: "Clearly I am not a socialist. I am a proud Conservative. What the letter writer was saying was my work can appeal across party lines". Labour Party candidate Jessica Asato said: "Local people won't forget she is one of the most loyal Conservative MPs and shows unwavering support for the vicious bedroom tax, tax cuts for millionaires and the swift march of the profiteers into the NHS. If this is socialism I'll eat my hat." In May 2014, she was awarded the Grassroot Diplomat Initiative Award under the Business Driver category for designing and conceiving the Norwich for Jobs campaign, which brought over 400 jobs and apprenticeships for young people in her constituency. She retained her Norwich North seat in the snap 2017 general election, taking 21,900 votes, ahead of Labour's Chris Jones by 507 votes. Following the election, she was appointed as Parliamentary Under Secretary of State for Northern Ireland working under James Brokenshire. In August 2019, Smith was the victim of an anthrax scare, in which a 40-year-old man in Barnstaple sent her a package of anonymous white powder.
Smith is an active volunteer and fundraiser for several charities including Cancer Research UK and Sport Relief. She is a keen cyclist and badminton player. She also enjoys life drawing and has posed as a model at classes. She is an atheist. In 2012, Smith proposed to financial consultant Sandy McFadzean, whom she had been dating for four months. McFadzean proposed to her in the "traditional style" the following day. In 2013, the couple married in South Runcton, and they had their first child, a son, in 2016. In 2019, their second child, a daughter, was born.