Sfetsas was born in Amfilochia and raised in Lefkada where, at an early age, he studied music for the first time at the Philharmonic Band and the National Conservatory of the city with the late Fotis Vlachos.
There, on a French State scholarship (1969–1972), he pursued further studies with the composer and educator Max Deutsch (composition, analysis, orchestral conducting), while seeking the mentorship and advice of Iannis Xenakis, Luigi Nono and Henri Dutilleux.
The first public performance of his work ("Episodes for piano solo") took place just after the uprising of May '68 at the "Latin America Hall" in Paris, receiving favourable reviews.
In addition, from its very early days, the Athens Concert Hall (Megaron) has on numerous occasions commissioned and hosted works by Kyriakos Sfetsas, performed by famous Greek and other soloists and ensembles, including the organist Daniel Chorzempa and the Camerata Orchestra.
In volume 9B of the Dictionary of World Biography, the music critic Giorgos Leotsakos notes, among other things: "No other Greek 'avant-garde' composer's return to tradition was more impressive than that of Sfetsas.
However, by replacing this 'hermetic' idiom with authenticated codes of communication, the music of Sfetsas expands sometimes into great lengths, and reveals a painful loneliness and a quest for the other, in which it is difficult to distinguish between the personal and the socio-environmental factors.