Diederik Rooker began his musical career at the Noord-Hollands Jongenskoor under the direction of Hendrik Timmerman performing as a boy soprano soloist. Later he took part in the World Youth Choir and World Voices, participating in various world tours. Diederik studied with Maria Rondèl, Paula de Wit, and Jón Thorsteinsson. In vocal ensembles Diederik sang under conductors such as Claudio Abbado, Rinaldo Alessandrini, Frieder Bernius, Frans Brüggen, Eric Ericson, Nikolaus Harnoncourt, René Jacobs, Tõnu Kaljuste, Simon Rattle, Daniel Reuss, Jordi Savall and Masaaki Suzuki.
As a soloist he has performed the oratorio repertoire of C.Ph.E. Bach, J.S. Bach, Luciano Berio, Reinhard Keiser, Felix Mendelssohn Bartholdy, Claudio Monteverdi, W.A. Mozart, Franz Schubert and Antonio Vivaldi.
Currently Diederik sings with Cappella Amsterdam, Collegium Vocale Gent, Pygmalion, La Capella Reial de Catalunya, the Nederlandse Bachvereniging, Laurens Collegium, Arnold Schoenberg Chor and Vocalconsort Berlin.