Callum was born in England. Soon after, his family moved to the west coast of Scotland. At an early age, Callum began working with the Scottish Youth Theatre in Glasgow. When he was eight-years-old, Callum and his family moved to America, living in a Vermont ski town. As a teenager, Callum spent one summer studying at the Circle in the Square Theatre School in New York City. He also spent two summers studying at the British American Drama Academy (BADA) in Oxford. After graduating high school, Callum returned to the UK to pursue a classical training at the Drama Centre in London. Since graduating, Callum has worked in film, television, and theatre in both the US and the UK.