He was born on October 9, 1964. He lived in St. Stephen, New Brunswick. He now lives in Toronto, Canada and regularly attends the Toronto Public Library.
Ralston's most notable roles are George Venturi on Life with Derek, and his role as Mr. Avenir on Strange Days at Blake Holsey High. Although John Ralston was born in Chatham, New Brunswick (Miramichi, New Brunswick), he grew up in Fredericton and St. Andrews, New Brunswick. He became interested in acting while going after a diploma in jazz studies at St. Francis Xavier University in Nova Scotia.
In 2006 and 2007, he was featured in Toyota Tundra truck commercials airing in Canada and starred as Ming the Merciless in the 2007 Sci-Fi Channel original series Flash Gordon. In 2008 he was in the Lifetime movie A Near Death Experience.