Wilhelm Killmayer was born in Munich on 21 August 1927. From 1945-1951 he was a music student at the music seminar of Hermann Wolfgang von Waltershausen. From 1951 to 1953 he had private lessons with Carl Orff and then attended Orff's master class at the Staatliche Musikhochschule in Munich. At the same time he studied musicology with Rudolf von Ficker and Walter Riezler, combined with studies in German at the University of Munich.

He taught theory and counterpoint at the Trapp Conservatory (1955 to 1958) and worked as a ballet conductor at the Bavarian State Opera in Munich from 1961-1964. From 1968 until 1975 Killmayer lived in Frankfurt on the Main as a free lance composer. During the years 1973-1993 he was professor of composition at the Staatliche Hochschule für Musik in Munich. In 1972 Wilhelm Killmayer became a full member of the Bavarian Academy of Fine Arts and since 1980 Killmayer has been a member of the Berlin Academy of Arts.

Killmayer has received numerous prizes for his extensive oeuvre; among others in 1954 the Prize of the Fromm Music Foundation in Chicago for his "Missa brevis", 1965 the Prix Italia for "Une leçon de français" and in 1974 the "Rostrum of Composers", Paris, for "Sinfonie I (Fogli)" and 2010 the Prize of the Christoph und Stephan Kaske Foundation. Wilhelm Killmayer lives in Munich and at the Chiemsee.