Sonja Behrens started performing for school radio and service organizations at the age of four. She was educated by the Sisters of the Holy Name at St. Mary's School of Music in Medford, Oregon, and graduated with highest honours from Willamette University in Salem, Oregon. She then became a scholarship student with Adele Marcus at the Juilliard School. During doctoral studies at Boston University, she received a Canada Council fellowship, the Aaron Richmond Scholarship, and the Aaron Richmond Prize for the most outstanding graduate pianist.

After graduation, Behrens held faculty positions at the Conservatory of Performing Arts, University of Regina (Regina Conservatory), Western Washington University, University of British Columbia, Simon Fraser University, California State University, University of California at Santa Barbara, Wilfrid Laurier University and the University of Western Ontario 1976-2003, where she administered the Fridays at Noon Series.

Behrens performed in solo recitals and with orchestras and chamber ensembles, for example, with Tsuyoshi Tsutsumi, and broadcast on radio and TV, including the CBC and WNYC New York. She recorded Hindemith's Sonata with the clarinetist Diane Lang Bryan (1983, Protone PR-157) and also recorded for the Eckhardt-Gramatté Foundation in Winnipeg. Behrens was an adjudicator, juror and consultant to arts organizations throughout the United States and Canada. She taught master classes and spoke at conferences on Liszt and Chopin. She co-ordinated the piano program for the Courtenay Youth Music Centre in British Columbia.

In 2003, Behrens performed and taught at Mount Allison University. She was a member of the Ontario Registered Music Teachers' Association.

Her husband was the teacher and composer Jack Behrens.