At 21, she moved to the Hochschule für Musik Freiburg, where she studied with Rainer Kussmaul; it was during this period that she developed an interest in the Baroque violin.
After graduation, she supplemented her training by working with Nikolaus Harnoncourt in Salzburg.
In 1987 she was co-founder of the Freiburger Barockorchester, whose musical direction she shares with her colleague Gottfried von der Goltz.
Petra Müllejans is Professor of Baroque Violin at the Hochschule für Musik Freiburg and at the Frankfurt University of Music and Performing Arts.
Müllejans also performs with a group called "Hot and Cool" in concerts and recordings of klezmer, tango, Czardas and jazz music.