Mendel studied until 1925 at Harvard University and then attended until 1927 courses in music theory with Nadia Boulanger in Paris. From 1930 to 1938 he was a member of the music publisher G. Schirmer, Inc.. Besides he worked from 1930 to 1933 as a music critic for the magazine The Nation. From 1940 to 1943 he was editor of the Journal of the American Musicological Society, and from 1941 to 1947 at the Associated Music Publishers.
From 1938 to 1950, Mendel taught at the Dalcroze School of Music, whose director he was from 1947, and the Diller - Quaile School in New York. He gave in 1949 at Columbia University and in 1951 at the University of California at Berkeley lectures. From 1952 until his retirement in 1973 he was a professor at the Faculty of Music at Princeton University, which he directed until 1967.
From 1936 to 1953 Mendel conducted the Cantata Singers in New York, one of the first authentic Baroque choirs in the United States. In 1945, he was out in New York The Bach Reader (2nd edition 1966 with Hans Theodor David). A collection of his articles and studies on the Renaissance and Baroque music, published in 1969 in the volume Studies in the History of Musical Pitch. Mendel was one of the editors of the New Bach Edition and Josquin edition. In addition, he edited Bach's Christmas Oratorio ( Christmas Story, 1949) and Musicalische funeral (1957). 1969-70 appeared his treatise on the use of computer technology in music Computers and the Humanities.