He has served as a government whip, and before entering politics he worked as a merchant banker.
Born in Bristol, Duddridge was educated at Crestwood School, Huddersfield High School and The Blue School, Wells. He read Government at the University of Essex.
Duddridge served as Chairman of the Wells Young Conservatives from 1989 until 1991, and was elected Chairman of Essex University's Conservative Association in 1990. In 1991, Conservative MP Bernard Jenkin appointed him as a researcher.
After graduating in 1993, Duddridge went on to pursue a successful business 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 highly successful national polling firm YouGov. He remains interested in financial matters and the effect of legislation on business.
Duddridge contested Rother Valley at the 2001 general election unsuccessfully for the Conservative Party, finishing second some 14,882 votes behind the sitting Labour MP, Kevin Barron but achieving a 5% swing in his favour. He was subsequently selected as the Conservatives' parliamentary candidate for Rochford and Southend East at the 2005 general election, following Sir Teddy Taylor's retirement. He held the seat for the Conservatives with a majority of 5,494 and delivered his maiden speech in the House of Commons on 9 June 2005.
From 2005 to 2007, Duddridge has served on the Environment, Food and Rural Affairs Select Committee, and the International Development Committee from 2006 to 2008, and in January 2008, he was appointed an Opposition Whip. He was returned at the 2010 general election again as Rochford and Southend East's MP, becoming a Lord Commissioner of the Treasury (Government Whip) with responsibility for the Foreign and Commonwealth Office and the Department for Education, but later left government in Prime Minister David Cameron's September 2012 reshuffle.
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.
Duddridge voted in favour of the Marriage (Same Sex Couples) Bill at both its second reading in February 2013 and its third reading in May 2013.
On 11 August 2014, it was announced that Duddridge would return to Government as Parliamentary Under-Secretary for Foreign and Commonwealth Affairs following the resignation of Mark Simmonds.
Duddridge is seen as a hardline Eurosceptic having suggested in Parliament that the Government should tell the European Commissioner to "sod off" rather than pay benefits to Romanians and Bulgarians.
On 9 February 2017, Duddridge tabled a 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", and received criticism from across the house.