Dr. Hendrickson practiced law in California for 31 years, and coincidentally with that practice obtained his PhD in psychology from Alliant International University and worked part-time in a private clinical psychology practice in Irvine, California for 13 years, with practice dedicated to serving persons with developmental disability. After he retiref from the practice of law in 2004, he worked for two years as a contract psychologist with the California Department of Coorections in Lancaster and Corcorarn. He has been a forensic evaluator with the Center for Forensic Services at Western State Hospital (WSH), and Washington Stat e Department of Social and Health Services (DSHS), since January 2006. He had been the Director of the WSH Postdoctoral Fellowship Committee from 2010 to 2018.

Dr. Hendrickson is an adjunct member at Antioch University Seattle, where he has taught forensic psychology, ethics, intelligence, and other treatment and assessment courses. He is a Clinical Associate Professor with the University of Washington School of Medicine, Department of Psychiatry and Behavioral Sciences. He taught law courses, including evidence, legal procedures, and family law, at the University of California, Irvine for more than 15 years until he moved to Washington State in 2006.