Born in Midland, Ontario, and raised in Paris, Ontario, Muckler was a defenceman in the minor leagues for 13 seasons, playing the bulk of his career in the old Eastern Hockey League (EHL). Muckler began his professional coaching career as a player/coach in 1959 with the EHL's New York Rovers. He then spent the next 20 years with the New York Rangers, Minnesota North Stars and Vancouver Canucks before joining the Edmonton Oilers organization in 1981. During those 20 years, Muckler served briefly as head coach of the Minnesota North Stars in 1968-69 and won multiple regular-season titles, playoff championships and league coach-of-the-year honours in the minor leagues. For his successes, The Sporting News named him the top coach in all of minor-league hockey in 1979.