At Gakushūin University, Viglielmo participated in a graduate seminar on Sōseki conducted by Sōseki biographer Komiya Toyotaka. In the spring of 1955 his Harvard teacher, Serge Elisséeff, asked Viglielmo if he would accept an appointment as a Harvard instructor in Japanese language and literature, beginning in Fall 1955. He taught at Harvard until June 1958, having completed his doctoral dissertation in December 1955 and having received his Ph.D. degree in March 1956. During the period from Fall 1958 until June 1960 he taught at International Christian University as well as Tokyo Women's Christian University and Tokyo University.