Derek was elected as Member of Parliament for West Cornwall and the Isles of Scilly (St Ives) in 2015 having grown up in West Cornwall. His work in Parliament includes responsibilities such as chair of the Brain Tumour All Party Parliamentary Group (APPG) and chair of the Diabetes APPG. He serves on the Environment, Food and Rural Affairs Select Committee and has a number of other minor responsibilities in relation to topics such as the Armed Forces, healthy homes, the environment and freedom of religion or belief. He is part of a cross-party fellowship group and has nurtured friendly relations with colleagues from all political parties.

He lives with his wife Tamsin, and their three children and together they worship at Discovery Church in Penzance. Prior to his work as MP, Derek has worked in the Christian voluntary sector and in the construction trade.