Although both parents of Wellesz's were Hungarian Christians, they both had Jewish ancestry. Even though he had Jewish ancestry and had a Protestant upbringing, he still later converted to Catholicism. Wellesz studied in Vienna under Arnold Schoenberg — purportedly his first private pupil — as well as Guido Adler, who founded the musicological institute in Vienna and was a leading editor of the Austrian Denkmaler. These dual influences shaped much of his musical and scholarly thought. In 1913, Wellesz embarked upon what would become a lifelong interest in the musical achievements of Byzantium.
Wellesz left Austria for England in the wake of the Anschluss — more specifically, Wellesz was in Amsterdam at the time by good fortune, to hear his orchestral piece Prosperos Beschwörungen conducted by Bruno Walter on that day. In England he was interned as an enemy alien, ultimately in Hutchinson Camp in the Isle of Man, but he gained his release in 1943 thanks to the intercession of H. C. Colles, the long standing chief music critic of The Times. Altogether he wrote nine symphonies and an equal number of string quartets, the former starting, in 1945, only with his arrival in England and the latter series of works spread throughout his life. Other compositions by him include operas, one of which (Die Bakchantinnen) was revived and recorded a few years ago; an octet with the same instrumentation as Schubert's; piano and violin concertos (one of each); and a suite for violin and orchestra. Stylistically his earliest music, somewhat like that of Ernst Krenek, is in a harsh but recognisably tonal style; there is a definite second period of sorts around the time of the first two symphonies (1940s) in which his music has a somewhat Brucknerian sound — in the symphonies sometimes an equal breadth, though still with something of a 20th-century feel and harmonies — but after his fourth symphony (the Austriaca) his music is more tonally vague in character, with serial techniques used. This idiom is consistent with hints of tonality, such as can be found in his eighth string quartet.
Despite his composing, Wellesz remains best known for his extensive scholarly contributions to the study of Byzantine music. These contributions brought for him an honorary doctorate from Oxford (where he later taught) in 1932.
Wellesz’s works as a composer amount to at least 112 works with opus numbers as well as some 20 works without opus number. He busied himself in a variety of media.
Recently, interest in Wellesz's music has increased. A complete recording of his nine symphonies is available, although his music has generally been sparsely represented on CD or LP. His 3rd symphony (1950-1), published posthumously, received its world premiere in Vienna in 2000. Several of his symphonies have titles, including the second (The English), and the seventh (Contra torrentum).
Works for Stage 
- Das Wunder der Diana, op. 18 (1914–1917), ballet after Béla Balázs
- Die Prinzessin Girnara, op. 27 (1919–1920), libretto by Jakob Wassermann
- Persisches Ballett, op. 30 (1920), ballet after Ellen Tels
- Achilles auf Skyros, op. 33 (1921), ballet after Hugo von Hofmannsthal
- Alkestis, op. 35 (1924), Libretto by Hugo von Hofmannsthal after Euripides
- Die Nächtlichen: Tanzsinfonien, op. 37 (1924), Ballet scene after Max Terpis
- Die Opferung des Gefangenen, op. 40 (1924–1925), Stage drama after Eduard Stucken
- Scherz, List und Rache, op. 41 (1927), libretto after Johann Wolfgang von Goethe
- Die Bakchantinnen, op. 44 (1931), libretto by the composer after Euripides, opera in 2 Acts
- Hymne der Agave aus Die Bakchantinnen, op. 44, concert edition by Wellesz
- Incognita, op. 69 (1950), libretto by Elizabeth MacKenzie and William Congreve
Choral Works 
- Drei gemischte Chöre, op. 43 (1930), text: Angelus Silesius
- Fünf kleine Männerchöre, op. 46 (1932) from Fränkischen Koran by Ludwig Derleth
- Drei geistliche Chöre, op. 47 (1932) for men's chorus based on poems from Mitte des Lebens by Rudolf Alexander Schröder
- Zwei Gesänge, op. 48 (1932) based on poems from Mitte des Lebens by Rudolf Alexander Schröder
- Mass in F minor, op. 51 (1934)
- Quant'è bella Giovinezza, op. 59 (1937), for women's choir
- Carol, op. 62a (1944) for women's choir
- Proprium Missae, Laetare, op. 71 (1953) for choir and organ
- Kleine Messe in G major, op. 80a (1958) for three similar voices a capella
- Alleluia, op. 80b (1958) for soprano or tenor solo
- Laus Nocturna, op. 88 (1962)
- Missa brevis, op. 89 (1963) for choir
- To Sleep, op. 94 (1965) for choir
- Festliches Präludium, op. 100 (1966) on a Byzantinium Magnificat for choir and organ
Orchestral Works 
- Heldensang, op. 2 (1905), symphonic prologue for large orchestra
- Vorfrühling, op. 12 (1912), symphonic mood picture for orchestra
- Suite, op. 16 (1913), for orchestra
- Mitte des Lebens, op. 45 (1931–32), cantata for soprano, choir, and orchestra
- Piano Concerto, op. 49 (1933)
- Amor Timido, op. 50 (1933), aria for soprano and small orchestra, text: Pietro Metastasio
- Prosperos Beschwörungen, op. 53 (1934–36), five symphonic works for orchestra after William Shakespeares The Tempest
- Lied der Welt, op. 54 (1936–38), for soprano and orchestra. Text: Hugo von Hofmannsthal
- Leben, Traum und Tod, op. 55 (1936–37), for alto and orchestra. Text: Hugo von Hofmannsthal
- Schönbüheler Messe C-dur, op. 58 (1937), for choir, orchestra, and organ
- Symphony No. 1, op. 62 (1945)
- Symphony No. 2, op. 65 (1947–48), The English
- Symphony No. 3, op. 68 (1949–51)
- Symphony No. 4, op. 70 (1951–53), Austriaca
- Symphony No. 5, op. 75 (1955–56)
- Violin concerto, op. 84 (1961), dedicated to the violinist Eduard Melkus. Recorded by David Frühwirth in 2010 on CD.
- Four Songs of Return, op. 85 (1961), for soprano and chamber orchestra, after texts by Elizabeth Mackenzie
- Duineser Elegie, op. 90 (1963) for soprano, choir, and orchestra after Rainer Maria Rilke
- Ode an die Musik, op. 92 (1965) for baritone or alto and chamber orchestra, text: Pindar, in free adaptation of works by Friedrich Hölderlin
- Symphony No. 6, op. 95 (1965)
- Vision for soprano and orchester, op. 99 (1966), text: Georg Trakl
- Mirabile Mysterium, op. 101 (1967) for soloist, choir, and Orchester
- Symphony No. 7, op. 102 (1967–68), Contra torrentem
- Canticum Sapientiae, op. 104 (1968) for baritone, choir, and orchestra after texts from the Old Testament
- Divertimento, op. 107 (1969), for small orchestra
- Symphonic Epilogue, op. 108 (1969)
- Symphony No. 8, op. 110 (1970)
- Symphony No. 9, op. 111 (1970–71)
Chamber Music 
- String Quartet No. 1, op. 14 (1912)
- String Quartet No. 2, op. 20 (1915–16)
- Geistliches Lied, op. 23 (1918–19) for singing voice, violin, viola, and piano
- String Quartet No. 3, op. 25 (1918)
- String Quartet No. 4, op. 28 (1920)
- Sonata for violoncello solo, op. 30 (1920)
- Two Works for clarinet and piano, op. 34 (1922)
- Sonata for violin solo, op. 36 (1923)
- Suite for violin and chamber orchestra, op. 38 (1924)
- Sonnet by Elizabeth Barrett-Browning for soprano and string quartet or large string ensemble, op. 52 (1934)
- Suite for violoncello solo, op. 39 (1924)
- Suite for violin and piano, op. 56 (1937/1957)
- Suite for flute solo, op. 57 (1937)
- String quartet No. 5, op. 60 (1943)
- The Leaden Echo and the Golden Echo, song for soprano, clarinet, violoncello, piano, op. 61 (1944), text: Gerard Manley Hopkins
- String Quartet No. 6, op. 64 (1946)
- String Quartet No. 7, op. 66 (1948)
- Octet, op. 67 (1948–49) for clarinet, bassoon, horn, two violins, viola, violoncello, and contrabass
- Sonata for violin solo, op. 72 (1953/59)
- Suite, op. 73 (1954) for flute, oboe, clarinet, horn, and bassoon
- Suite for solo clarinet, op. 74 (1956)
- Suite for solo oboe, op. 76 (1956)
- Suite for solo bassoon, op. 77 (1957)
- Fanfare for solo horn, op. 78 (1957)
- String Quartet No. 8, op. 79 (1957)
- Quintet, op. 81 (1959) for clarinet, 2 violins, viola, and violoncello
- String trio, op. 86 (1962)
- Rhapsody for viola solo, op. 87 (1962)
- Musik for string orchestra in one movement, op. 91 (1964)
- Fünf Miniaturen for violins and piano, op. 93 (1965)
- Partita in Honor of Johann Sebastian Bach, op. 96 (1965) for organ
- String Quartet No. 9, op. 97 (1966)
- Four Works for string quartet, op. 103 (1968)
- Four Works for string trio, op. 105 (1969, second version 1971)
- Four Works for string quintet, op. 109 (1970)
- Prelude for viola solo, op. 112 (1971)
Decorations and awards 
- 1953: City of Vienna Prize for Music
- 1957: Commander of the Order of the British Empire
- 1957: Great Silver Medal of the City of Paris
- 1959: Grand Decoration of Honour in Gold for Services to the Republic of Austria
- 1961: Grand Austrian State Prize for Music
- 1961: Order of St. Gregory the Great (Vatican)
- 1971: Austrian Decoration for Science and Art
- 1973: Honorary Member of the Society of Friends of Music in Vienna
- Benser, Caroline Cepin (1985). Egon Wellesz (1885-1974) : chronicle of twentieth-century musician. New York: P. Lang. ISBN 0-8204-0138-2.
- Wellesz, Egon; Kerridge, W. H., translator (1925?). Arnold Schönberg. London: J. M. Dent & Sons. OCLC 23799320.
- Wellesz, Egon (1960). New Oxford history of music 1. Ancient and oriental music. Oxford: Oxford University Press. OCLC 174194430.
- Wellesz, Egon (1961). A history of Byzantine music and hymnography. Clarendon Press. OCLC 3309386.
- Wellesz, Egon (1965). Fux. London; New York: Oxford University Press. OCLC 302872.
- Wellesz, Egon; Conomos, Dmitri; Velimirović, Miloš (1966). Studies in Eastern Chant. London; New York: Oxford University Press. ISBN 0-913836-79-6. OCLC 1126942.
- Krones, Hartmut (2001-12-05). "Notes to US Premiere of Wellesz Symphony 3". American Symphony Dialogues and Extensions. Retrieved 2007-12-22.
- Amanda Holden remembers Egon Wellesz
- Conway, Paul (June 1999). "An Austrian Symphonist in Britain". MusicWeb International. Retrieved 2007-12-22.
- Conway, Paul (July 2000). "The long-awaited world premiere of the third symphony triumphs in Vienna". MusicWeb International. Retrieved 2007-12-22.
- Robert Scholium, "Egon Wellesz, Osterreichische Komponisten des XX. Jahrhunderu, II (Vienna, 1964)
- Hans F. Redlich, "Egon Wellesz," The Musical Quarterly, XXVI (1940), 65-75
- Rudolph Reti, "Egon Wellesz, Musician and Scholar," ibid., XLII (1956), 1-13.
- Klavierkonzert/Violinkonzert, Babinsky (piano), Frühwirth (violin), Epple (conductor), Egon Wellesz (composer)