Former Borehamwood Labour councillor Frank Ward ran for Ukip, winning 6,383 votes, while Liberal Democrat candidate Sophie Bowler - who works in anti-money laundering - held on to her deposit with 2,777 votes.
Hertsmere, the fastest-growing Jewish area in Britain, has been a Tory stronghold ever since the constituency was created in 1983.
Mr Dowden, 36, will represent the third-most Jewish constituency in Britain, with members of the community making up 14.3 per cent of Hertsmere’s population.
The married father-of-two was born and raised in Hertfordshire, and placed local issues such as protecting the countryside and improving transport links at the heart of his campaign.
A Cambridge graduate before working as a lawyer, he began his political ascent in the party's research unit under Michael Howard's leadership ahead of the 2005 election.
Voter turnout in the constituency was 68.3 per cent, up from 65 per cent in 2010.
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