Kai Wessel started singing in school choirs and as a boy soprano at the Christus-Kirche of Hamburg-Wandsbek and received lessons on piano, organ and oboe.
He studied to become a composer at the Lübeck Academy of Music but then concentrated on training his countertenor voice with Ute von Garczynski.
From 1994 to 2004, he was engaged at the theatre of Basel where he sang in productions of Herbert Wernicke in Handel's Theodora, Giulio Cesare and Israel in Egypt, among others.
He took part in the project of Ton Koopman to record the complete vocal works of Johann Sebastian Bach with the Amsterdam Baroque Orchestra & Choir.
Composers such as Mauricio Kagel, Karola Obermüller, Chaya Czernowin, Heinz Holliger and Klaus Huber wrote works for him.