One of nine children in the McDonnell family, Mike received his first easel at age four. At age thirteen, McDonnell moved out of his parents' home and lived in various places before graduating from Fremont High School in 1956. After graduation, McDonnell moved to Chicago and attended the American Academy of Art for two years. In 1958, McDonnell moved to New York and attended at the Art Students League for two years, and National Academy of Design for a year. In 1961, McDonnell was drafted into the United States Army and worked as a draftsman for two years before his discharge. In 1963, McDonnell moved to Flint, Michigan where he worked as an office interior illustrator and did painting during the rest of his free time. After a brief period of living in New York in 1963, McDonnell moved back to Michigan and in 1965 he met his future wife, Karen Mathieson, on Mackinac Island. The couple married in June 1966 near Frankfort, Michigan, and settled on a nearby farm. The couple later moved to Kaleva, Michigan.