John was born in Miramichi, New Brunswick, on October 9, 1957. He is the youngest of the four children of Mary and James (Bill) Ralston. His father was a decorated Second World War and Korean War pilot, who was interned in a German PoW camp from April 1942 until April 1945. After his father retired from the Air Force, John's family settled in Fredericton and spent summers in St. Andrews By-the-Sea. John attended the University of New Brunswick and received a Bachelor of Education degree in Literature and Anthropology. After teaching on a First Nations Mi'kmaq reserve in Nova Scotia, John followed a latent interest in music and enrolled in a Jazz Studies diploma program at St. Francis Xavier University in Antigonish, Nova Scotia. While there, he was introduced to a thriving theatre scene. He soon found himself on stage, and was noticed immediately in productions of Godspell and Othello. Director Maxim Mazumdar invited John to Newfoundland, where he really cut his teeth in repertory and regional theatre. He then continued working across Canada and abroad in every stage genre, from classical to modern and contemporary drama and comedy.
After settling in Toronto, John decided to focus more on acting for film and television. He has worked steadily in film and television, compiling an impressive and eclectic list of credits. He is also sought after in the world of narration and documentaries.
John is married to actress Karen Waddell. They have two children and live in Toronto