Ellwood was elected as a Councillor of Dacorum Borough Council in Hertfordshire in 1999, and unsuccessfully contested the parliamentary seat of Worsley in Manchester at the 2001 general election being defeated by the sitting Labour MP Terry Lewis by 11,787 votes. He achieved success at the 2005 general election, when selected to contest the safe Conservative seat of Bournemouth East to succeed the outgoing David Atkinson MP. Ellwood held Bournemouth East with a majority of 5,244 votes and remains the MP there. He made his maiden speech in the House of Commons on 19 May 2005.