At different times in his career, he lectured at Columbia University, the University of Chicago, and the University of California at Los Angeles.
His 1962 La Religion de l’Iran Ancien is still considered a masterpiece and the best scholarly introduction to Zoroastrianism despite the decades of subsequent developments in the scholarship of the religion.
His international reputation culminated in his appointment, in 1973, as editor of the series Acta Iranica.In 1974, he was awarded an honorary doctorate from the University of Tehran.