Veteran of World War II, a historian of antisemitism, and a medievalist at Stanford University.
He initially planned a military career, and served as a lieutenant in the Canadian Army's Royal Highland Regiment during World War II.
However, his interests shifted to medieval studies; in 1955 he completed his doctoral program with a dissertation on English constitutional history.
He wrote many academic articles and two books on the history of medieval Jews and anti-Semitism.
[1] Langmuir's research received critical praise from many scholars: In a book published in the year before Langmuir died, Christopher Browning attributes to him the concept of "xenophobic anti-Semitism," a socially motivated rather than religiously motivated attitude that according to Langmuir should be distinguished from a traditional hostility to Judaism that Christianity inherited from a long history of religious differences.