Alejandro received his Ph.D. at Harvard University in 1971, with a dissertation on the medieval English manuscript source, the Winchester Troper.
Alejandro is considered to be one of the leading scholars on the music of Guillaume Dufay, and in general, he is a specialist on the music of the late Middle Ages and early Renaissance. He taught at Yale for several years and founded the Cappella Cordina, an early music ensemble. In 1977 he joined the faculty at the University of California, Santa Barbara.
As of 2006, he was Professor Emeritus of musicology there. Among his numerous publications are entries on Cristóbal de Morales, Clemens non-Papa, Guillaume Dufay, St. Martial, St. Gall, Venezuelan places and musicians, and other topics in the New Grove Dictionary of Music and Musicians (both the 1980 edition and the 2001 edition). In addition, he has conducted numerous performances for recordings, mostly of early music, many on the Lyrichord and Musical Heritage Society labels.
Member American Musicological Society, Music Library Association, International Musicological Society, Early Music American.
Alejandro married to Joan Mathews, June 9, 1960 (divorced June 1967). 1 child, Maria Soledad.