Greek mezzo-soprano Nefeli Kotseli was born in Athens, where she studied piano, music theory and singing at the Athens National Conservatory (graduating with honours and first prize for best performance). She continued her postgraduate studies at the University of Music and Performing Arts in Vienna with Gabriele Lechner and in song/oratorio with Anton Scharinger. There she sang Mercédès (Carmen), Cornelia (Giulio Cesare in Egitto), Sesto (La clemenza di Tito) and Charlotte (Werther). She also sang the role of the Third Lady in Die Zauberflöte at the Schönbrunn Palace Theatre in Vienna, the role of Smaragda in the children's opera Der Tulifant by Gottfried von Einem and the role of Miss Newkirk in the children's opera Help, Help the Globolinks by Menotti, both at the MuTh Theatre in Vienna with the Vienna Boys' Choir. In 2023, she made her debut at the Greek National Opera in the role of Neris in Cherubini's Medea, conducted by Philippe Auguin. She then appeared as Ethel in Les Eclairs by Philippe Hersant at the Greek National Opera. 

Nefeli has also performed numerous concert roles, including in works such as Mozart's Requiem, Verdi's Messa da Requiem, Bach's Christmas Oratorio, Handel's Messiah, Pergolesi's Stabat Mater and Beethoven's 9th Symphony with the Vienna Philharmonic. She also sang the mezzo-soprano solo in Vijay Upadhyaya's Symphony No. 1 Prayer Flags with the China National Symphony Orchestra at the Beijing Concert Hall. In 2021, Nefeli made her debut at the Vienna Musikverein as alto soloist in Mahler's Symphony No. 2 with the Vienna Philharmonic under the baton of Vijay Upadhyaya. Kotseli's engagements in the 2024/25 season included roles such as Waltraute in Die Walküre in a production by the Greek National Opera, as well as appearances in Mahler's Symphony No. 2 at the Megaron Athens Concert Hall conducted by Christoph Eschenbach and Mahler's Symphony No. 8 at the Vienna Konzerthaus conducted by Vijay Upadyaya. Nefeli Kotseli has been a member of the Dortmund Opera ensemble since April 2026.