Born in Neuruppin, Koegler studied musicology, German and art history in Kiel from 1945 to 1946 and directing, dramaturgy and acting at the newly founded Staatliche Hochschule für Theater und Musik Halle [de] in Halle an der Saale from 1947 to 1949.
He then received a three-year engagement at the Gerhart-Hauptmann-Theater Görlitz-Zittau [de] as assistant dramaturg and director.
Since moving to West Berlin in 1951, he worked as a freelance journalist and writer, increasingly for English-language magazines.
He first gained access to his later focus on dance as a reporter of Berlin opera performances.
As a consequence, "an artificially imposed schism between ballet and dance theatre [...] arose that was nowhere else pursued as doggedly as in this country".