A vocal defender of francophone rights outside Quebec, Marion is best known for his research on French Canadian literature.
Marion grew up at 113 College St., now the corner of Louis-Pasteur Pvt. and Marie-Curie Pvt. On what is now the University of Ottawa campus. After graduating from the local primary school, École Garneau, he did his high school (cours classique) at the University of Ottawa and eventually earned a Masters degree in French Literature in 1918. It was a simpler time and there were no courses to follow, just a thesis to write. Marion recalls how one day the Rector just told him that he had read his thesis and that, in his opinion, it deserved the degree.
After receiving his doctorate from the Université de Paris, he taught French at the Royal Military College, Kingston (1920-1923). He then became head translator and later Director of historical publications at the Public Archives of Canada (1923-1953). In his work as an archivist, he discovered troves of little-known information on French-Canadian literature. Later, he taught French-Canadian literature at the University of Ottawa and presented the fruits of his research in some 20 studies, including a nine-volume collection entitled Les Lettres canadiennes d’autrefois.
A member of the Royal Society of Canada (1934), the Académie canadienne-française and the Société des Dix (1962), Séraphin Marion lectured all over Canada on the rights of Canada’s French-speaking minorities. Over the course of his career, this writer and scholar received numerous awards and honours, including Officer of the Order of Canada. An Ottawa primary school and a street (on the University of Ottawa campus) have been named in his honour, and the Société Saint-Jean-Baptiste de Montréal annually awards the Prix Séraphin-Marion.
 Marion describes his time at École Garneau (613 Cumberland) in a memoir he wrote in 1977, «De l’école Garneau à l’Université d’Ottawa au début du siècle», témoignage de Séraphin Marion sur l’enseignement des Soeurs Grises de la Croix à l’école Garneau d’Ottawa au début du XXe