Born in Quebec City, Canada, Johnston was raised in a military family and moved frequently before settling in Kingston, Ontario. She earned a degree in French from Concordia University after a course of study that included a year abroad at the Sorbonne, Paris. Her formal schooling in ceramics occurred at Sheridan School of Craft and Design. Johnston taught ceramics at her studio in Paris, Ontario for 10 years while continuing to develop her own work. With her husband John and four children, she moved to Carmel-by-the-Sea, California in 2013 and became a member of the Peninsula Potters Co-operative while building her own home studio.