Cowan paused his college education at the University of Utah to serve as a missionary of the Church of Jesus Christ of Latter-day Saints in Germany (Gleiwitz, Breslau, Magdeburg, Erfurt), acquiring considerable proficiency in the language.
In 1942, Cowan moved to Washington, D.C., to work as director of the Intensive Language Program of the American Council of Learned Societies, which under wartime circumstances was closely linked with the Army Specialized Training Program for 29 strategic languages conducted at numerous land-grant universities.
These included Cornell University, where Russian and Italian were taught under Army auspices, and in 1946 Cowan was appointed director of Cornell's newly established Division of Modern Languages (DML) to adapt the military's intensive language instruction methods to the regular university curriculum.
Cowan held a number of service positions throughout his life, becoming the president of the Linguistic Society of America in 1966.
His principal publication is the Dictionary of Modern Written Arabic (1961), a revised and expanded English-language version of Hans Wehr's original German Arabisches Wörterbuch für die Schriftsprache der Gegenwart (1952).