Liddell-Grainger unsuccessfully contested the seat of Torridge and West Devon for the Conservative Party at the 1997 general election, coming second to the Liberal Democrat candidate John Burnett. However, he was elected to parliament at the 2001 general election for the safe Conservative seat of Bridgwater in Somerset, succeeding former cabinet minister Tom King. He held the seat at the 2005 general election before boundary changes created the new seat of Bridgwater and West Somerset which he retained with a nominally reduced share of the vote at the 2010 general election. He was re-elected at the 2015 general election and 2017 general election.