Pet Halmen gained experience with designing sets at Deutsche Opera Berlin, and also worked with numerous designers in Düsseldorf, Munich and Schwetzingen. After this, he worked as a set and costume designer at Deutsche Oper am Rhein in Düsseldorf. His joint work with Jean-Pierre Ponnelle, including their 1975 Monteverdi cycle for Oper Zürich and their L'elisir d'amore for the Staatsoper Hamburg, gained international attention. Halmen designed the costumes for Götz Friedrich's 1981 film Elektra. Since 1986, he has also worked as a director, including on stages in New York, Paris, Toulouse, Nice, Tokyo, Pretoria, Madrid and Vienna.