Duddridge served as Chairman of the WellsYoung Conservatives from 1989 until 1991, and was elected Chairman of Essex University's Conservative Association in 1990. In 1991, whilst at university, local Conservative MP Bernard Jenkin appointed him as a researcher.
After graduating in 1993, Duddridge went on to pursue a career in the private sector. He was a banker with Barclays in the City of London and Africa for 10 years, rising to National Sales Director in the Ivory Coast and eventually running the bank's operations in Botswana with a staff of 750 people. He was also a founder member of the polling firm YouGov.
On 3 December 2010, Duddridge was permitted to reply on HM Government's behalf from the Despatch Box during an Adjournment debate, a rarity as Commons Whips – particularly Government Whips – by convention do not speak in the Chamber.[8]
Duddridge is seen as highly Eurosceptic, having suggested in 2013 that the Government should tell the European Commissioner to "sod off" rather than pay benefits to Romanians and Bulgarians.[11]
In September 2014, Duddridge claimed £11,348 for accommodation in London on expenses, mostly for hotels, despite already owning two homes in the city. He stated that his claims were in accordance with the Independent Parliamentary Standards authority.[13] The previous year, it was reported that he had the highest expenses claim of local MPs in Essex.[14] He was accused by Ian Kennedy of pursuing a "squalid vendetta" after he helped block the former head of the Commons expenses watchdog from an appointment to a new job of electoral commissioner in January 2018.[15]
At the 2015 general election, Duddridge was again re-elected, with a decreased vote share of 46.4% and a decreased majority of 9,476.[16][17]
On 9 February 2017, Duddridge tabled an Early Day Motion following comments made by Commons speaker John Bercow on the subject of the pending state visit of US President Donald Trump. The motion proposed "that this House has no confidence in Mr Speaker",[18] and received criticism from across the house.[19] The bid to remove Bercow as Commons Speaker failed after just five MPs backed Duddridge's motion of no confidence.[20]
Duddridge was again re-elected at the snap 2017 general election, with an increased vote share of 48.7% and a decreased majority of 5,548.[21]
On 27 September 2017, The Times reported that Duddridge, who had been Parliamentary Under-Secretary of State for Africa until 2016, was being paid £3,300 for eight hours' work a month as a consultant for Brand Communications on top of his MP's salary. The newspaper reported that this had led to renewed calls to review the rules surrounding jobs for former members of government. It was reported that he was working for Brand Communications and that the company was one of a handful that had not agreed to the industry's code of conduct that bans hiring sitting MPs. Duddridge told The Times: "The work I do involves helping companies going into the African marketplace re-brand themselves. It is not a public affairs role."[22]
At the 2019 general election, Duddridge was again re-elected, with an increased vote share of 58.7% and an increased majority of 12,286.[24]
On 4 July 2021, he attended the funeral of Kenneth Kaunda as Parliamentary Under-Secretary of State for Africa, and incorrectly identified Kaunda as Zimbabwean rather than Zambian.[25]
On 6 July 2022, following the mass resignation of members of the Johnson government, Duddridge was involved in an on-air argument with Piers Morgan during an appearance on an edition of talkTV's Piers Morgan Uncensored when he refused to answer questions from Morgan. Duddridge had been sent out from 10 Downing Street to speak in defence of Prime Minister Boris Johnson, but while he said he was happy to speak to the channel's political editor, Kate McCann, he refused to take questions from Morgan, claiming his wife would divorce him if he did. This resulted in the presenter labelling him an "impertinent little twerp", with Morgan later describing the moment as his "favourite TV encounter ever".[26]