Callum was born in Worcestershire, England. Soon after, his family moved to Scotland, residing on the West Coast. When Callum was three-years-old, he began working with the Scottish Youth Theatre in Glasgow, and continued this up until the age of eight. Callum then moved with his family to America, living in a picturesque ski town in the state of Vermont. In 2012, Callum returned to the UK to pursue a classical training at the prestigious Drama Centre London, where he graduated in 2015.