Oskar Seidlin joined the faculty at IU Bloomington in 1972, received the title of distinguished professor of Germanic languages in 1974, and retired in 1979 with the title of distinguished professor emeritus of Germanic languages. During his forty years in academia, he taught German language and literature at Smith College (1939-1942), German Summer Schools at Middlebury College (through 1957), at the Ohio State University (1946-1972), and at IU (1972-1979). For four years during World War II, Seidlin served in the U.S. Army. He took part in the invasion of Europe in the beginning of the war and revived and reorganized newspapers and radio stations in Germany during the end of the war. He received a Ph.D. summa cum laude in 1935 from the University of Basel (Switzerland).
Seidlin was an educator, literary scholar, and author, who wrote over 150 reviews and articles over the course of his career. A number of these were later published in English in Essays in German and Comparative Literature (1961) and in German in Von Goethe zu Thomas Mann (1963). Seidlin stated in the history of the OSU German Department, which he wrote, that he was probably best known for An Outline History of German Literature (1948), a volume he collaborated on with Werner P. Friederich and Philip A. Shelley.
Seidlin received numerous international and national awards during his academic career. He received two John Simon Guggenheim Memorial Foundation Fellowships in German and Scandinavian literature (1962, 1976), the Goethe Medal from the Goethe Institute for performing outstanding service for the German language and for international cultural relations (1963), an honorary doctorate from the University of Michigan in Ann Arbor (1968), and the Friedrich Gundolf Prize from the German Academy for Language and Literature for furthering understanding of German culture and cultural dialogue abroad (1968).
Seidlin passed away on December 11, 1984, in Bloomington, Indiana.