Xenakis was born in Brăila, Romania to Clearchos Xenakis and Fotini Pavlou, and was educated as a child by a series of governesses. At the age of ten he was sent to a Boarding school on the Aegean island of Spetsai, Greek and later studied Architecture and Engineering in Athens. Xenakis participated in the Greek Resistance during World War II and during the period of the British martial law , in the first phase of the Greek Cs Stratos, Greek People's Liberation Army). He received a severe face wound from a British shell which resulted in the loss of eyesight in one eye. In 1947 he fled under a false passport to Paris. In the meantime, in Greece he was sentenced In absentia to death by the rightwing administration. In Paris he worked with Le Corbudfasdfsadfsadsier. While his assistant, Xenakis designed the Pavillon Philips in Brussels, home of the première of Edgard Varèse's Poème Électronique at the 1958 Brussels International Fair. The Pavillon's hyperbolic structure was, in fact, based on the formative structure of one of his most famous pieces, "Metastaseis," composed some four years earlier. The dual nature of "Metastaseis" and the Pavillon are an example of Xenakis' theory of meta-art – the concept that an artistic expression can be realized mathematically in any artistic medium. Xenakis performed at many world expositions and fairs, and played annually in the Shiraz Art Festival in Iran.
Xenakis's primary teachers of composition were Aristotelis Koundouroff, Arthur Honegger, Darius Milhaud, and Olivier Messiaen. His own early compositions, however, rarely followed the rules he was being taught . His first meeting with Honegger exemplifies his attitude toward formal instruction: asked to play one of his compositions on the piano, Xenakis was stopped promptly as Honegger pointed out Parallel fifths and Octaves. Xenakis had written them intentionally and refused to "correct" the piece. Honegger attempted to humiliate Xenakis, who simply left to study with Milhaud. However, he believed Milhaud's teaching also imposed restrictions he found arbitrary and inessential.
Meanwhile, he continued to work full-time as an architect in Le Corbusier's employ, composing only as a hobby. Xenakis was a creative architect, exploring the possibilities of new materials and shapes in construction, and was frequently entrusted with important projects that called on his technical and artistic skills. Le Corbusier, who came from a musical family (and pretended to hate music) also mentored Xenakis as a composer; he regarded Xenakis and Varèse as two of France's most innovative and promising.
Later, Xenakis approached Olivier Messiaen for compositional advice, expecting to have to start his musical studies again from the beginning, but was told "No, you are almost thirty, you have the good fortune of being Greek, of being an architect and having studied special mathematics. Take advantage of these things. Do them in your music." Messiaen, whose own compositional style did not follow established precedents, did not try to impose the limitations of baroque counterpoint or Serialism as previous teachers had, but rather let Xenakis find his own musical ideas and guided them along. Xenakis attended Messiaen's Paris classes regularly, and his confidence grew along with his compositional skill; he would shortly thereafter combine the mathematical ideas he had been developing in Corbusier's studio with the musical tools he had been honing with Messiaen to produce his first major work.
He is particularly remembered for his pioneering electronic and Computer music, and for the use of Stochastic mathematical techniques in his compositions, including Probability. He explored the use of the Maxwell-Boltzmann kinetic theory of gases in Pithoprakta, Aleatory distribution of points on a plane in Diamorphoses, minimal constraints in Achorripsis, Gaussian distribution in ST/10 and Atrèes, Markov chains in Analogiques), Game theory (in Duel and Stratégie), Group theory (Nomos Alpha), and Boolean algebra (logic) (in Herma and Eonta), and Brownian motion (in N'Shima). In keeping with his use of probabilistic theories, many of Xenakis's pieces are, in his own words, "a form of composition which is not the object in itself, but an idea in itself, that is to say, the beginnings of a family of compositions."
In 1962 he published Musiques formelles, a collection of essays on his musical ideas and composition techniques. This was later revised, expanded and translated into Formalized Music: Thought and Mathematics in Composition in 1971.
In 1966, Xenakis founded the Centre for Automatic and Mathematical Music in Paris and subsequently set up a similar centre at Indiana University.
From 1975 to 1978 he was professor of music at Gresham College, London, giving free public lectures.
"By 1979, he had devised a computer system called UPIC, which could translate graphical images into musical results, wrote Andrew Hugill in 2008. "Xenakis had originally trained as an architect, so some of his drawings, which he called 'arborescences', resembled both organic forms and architectural structures." These drawings' various curves and lines that could be interpreted by UPIC as real time instructions for the sound synthesis process. The drawing is, thus, rendered into a composition. Mycenae-Alpha was the first of these pieces he created using UPIC as it was being perfected.
In 1982 Xenakis developed his now renowned Music Timbre and Cadence Scale which is used throughout the research of modern music for quantifying musical styles.
He was married to writer Françoise Xenakis, née Gargouïl. They had a daughter, painter and sculptor Mâkhi Xenakis.
He died in Paris in 2001.
In conversation, Iannis Xenakis frequently distanced himself from being seen in too strict terms - like many other composers for whom method and structure were the easiest aspects of music to discuss verbally, he sees the role of such things as relative. One way to envisage this approach is that the method constitutes a thematic germ, a starting-point, and from there the normal musico-aesthetics, personal obsessions and practical considerations play their normal role in finishing and shaping the piece. Indeed from the 1970s onwards Xenakis' use of method became deeply assimilated into his general musical thinking and he reports in interviews from that time that the strict application of statistical processes was no longer necessary to produce the results he was looking for.
Xenakis appeared easily bored in interviews when people attempted to take an overly simplistic view of him as 'complex' - the various clichés surrounding him appeared to greatly annoy him in interview and he would frequently make recourse to the wider Aesthetics of music in general and the other arts, in order to contextualise his contributions to music-making. In a sense his early statements about "looking at music statistically" were a response to what he saw as the mistake of placing too much emphasis on the likely benefits of applying methodology too rigorously. It is also important to note, however, that this does not constitute any true dichotomy between Xenakis and his peers - the application of single-minded rigour to composition in post-war music was relative and momentary, and as with his own work, the poetic and aesthetic significance of the gesture as a modern equivalent to programme-music, as well as the vital role played by musicality and music-editing/shaping has been widely undervalued in favour of simplistic characterisations of such music as purely intellectual.
Overall then Xenakis' contribution to the modernist aesthetic arose from the understanding that things which happen according to rules can be changed without loss of overall meaning, and developed (immediately) into a freeform polyphonic style focusing on large-scale emotional control and a generalistic approach to melody.
Another glaringly obvious but often overlooked aspect of Xenakis' work is the kind of neo-classical naming convention. Many essays have been written about the formula titles of his numbered works but it seems very clear that his obsession in most of his titles was with ancient Greece.
- Metastasis (Xenakis composition) (Metastaseis B') (1953-1954), for orchestra of 61 instrumentalists
- Pithoprakta (1955-1956), for orchestra of 50 instrumentalists
- Achorripsis (1956-57), for 21 instrumentalists
- Eonta (1963), for piano and 5 brass instruments
- Oresteïa (1965-1966), on texts from Aeschylus, suite for children's choir, mixed choir with musical accessories and ensemble of 12 musicians
- Terretektorh (1965-1966), for 88 musicians dispersed among the audience
- Medea (1967), scene music on texts from Seneca, for male choir playing rhythms with cymbals and 5 musicians
- Nomos Alpha (1966), for solo cello
- Polytope de Montréal (1967), spectacle of light and sound for 4 identical orchestras of 15 musicians
- Nuits (1967), on Sumerian, Assyrian, Achaean and other Phonemes, for 12 mixed solo voices or mixed choir
- Nomos Gamma (1967-1968), for 98 musicians dispersed among the audience
- Anaktoria (1969), for ensemble of 8 musicians
- Kraanerg (1968-1969), ballet music, for orchestra and four-channel tape
- Persephassa (1969), for 6 percussionists
- Persepolis (1971), for light and sound (eight-channel tape)
- Cendrées (1973), for mixed choir of 72 (or 36) singers chanting phonemes by Iannis Xenakis and 73 musicians
- Evryali (1973), for piano solo
- N'Shima (1975), on Hebrew words and phonemes, for 2 mezzo-sopranos (or altos) and 5 musicians
- Psappha (1976), for percussion solo (variable instrumentation)
- Dmaathen (1976), for oboe and percussion
- Kottos (1977), for solo cello
- Jonchaies (1977), for orchestra of 109 musicians
- Pléïades (1978), for 6 percussionists
- Pour Maurice (1982), for baritone and piano
- Shaar (1983), for large string orchestra
- Keren (1986), for solo trombone
- Jalons (1986), for ensemble of 15 musicians
- Keqrops (1986), for solo piano and orchestra of 92 musicians
- Kassandra (Oresteïa II) (1987), for amplified baritone (also playing a 20-string Psaltery) and percussion
- Rebonds (a + b) (1987-89), for percussion solo
- Xas (1987), for saxophone quartet
- La Déesse Athéna (Oresteïa III) (1992), for baritone solo and mixed ensemble of 11 instruments
- Amagali, Rosemary Tristano. 1975. "Texture as an Organizational Factor in Selected Works of Iannis Xenakis". M.M. Thesis, Indiana University.
- Baltensperger, André. 1995. Iannis Xenakis und die Stochastische Musik - Komposition im Spannungsfeld von Architektur und Mathematik. Zürich. Paul Haupt.
- Bardot, Jean-Marc. 1999. "Cendrées de Xenakis ou l'émergence de la vocalité dans la pensée xenakienne." Undergraduate thesis (equivalent). Saint-Etienne: Université Jean Monnet.
- Biasi, Salvatore di. 1994. Musica e matematica negli anni 50-60: Iannis Xenakis. Bologne. Università degli Studi di Bologna.
- Harley, James. 2004. Xenakis: his life in music. London: Taylor & Francis Books. ISBN 0-415-97145-4
- Mâche, François-Bernard. 2002. Portrait(s) de Iannis Xenakis Seuil. ISBN 2-7177-2178-9
- Matossian, Nouritza. 1990. Xenakis. London: Kahn and Averill. ISBN 1-871082-17-X
- Varga, Bálint András. 1996. Conversations with Iannis Xenakis. London: Faber and Faber. ISBN 0-571-17959-2
- Xenakis, Iannis. 2001. Formalized Music: Thought and Mathematics in Composition (Harmonologia Series No.6). Hillsdale, NY: Pendragon Press. ISBN 1-57647-079-2
- List of Gresham Professors of Music
- Xenakis Ensemble
- Institute of Research on Music and Acoustics, Athens (Greece): Iannis Xenakis Pages (with several sound and score samples)
- Iannis-Xenakis.org by the Friends of Xenakis
- Centre for Composition of Music Iannis Xenakis
- Medieval.org: Modern Music: Xenakis
- Edward Childs, PhD. "Achorripsis: A Sonification of Probability Distributions" (5-page PDF)
- Luque, Sergio. 2006. Stochastic Synthesis: Origins and Extensions. Masters Thesis, Institute of Sonology
- Works catalogue (70-page PDF) from Xenakis' publisher Éditions Durand-Salabert-Eschig
- Iannis Xenakis: the aesthetics of his early works by Markos Zografos