In 2000, Stephen was selected as Conservative Candidate for the Preseli Pembrokeshire constituency to contest the 2001 General Election. After a strong campaign he succeeded in reducing the Labour majority from 8,736 to 2,946 a swing of 6.3%, the largest in Wales.
He was selected again in 2003 to fight the seat for the 2005 General Election and was elected with a majority of 607 making him the youngest Conservative MP currently at Westminster.
Since the election, Stephen has taken a full and active role in Parliament, with voting records in the top 10% of all MPs. He is a member of the Welsh Affairs Select committee, sits on the Parliamentary Youth Affairs and British Dental Association Groups. He shares his office with David Jones MP, David Davies MP and Daniel Kawczynski MP at Westminster.
In January 2009, Stephen became an Opposition Whip.