Giel has a background in social cognition and did his PhD on the topic of goal contagion (i.e. unintentionally copying the social goal of another) at he University of Utrecht. He has worked for TNO (Prevention, Work, and Health) as an applied researcher, and as a lecturer in research methods and psychology at the Wageningen University and the Radboud University Nijmegen. Currently he does most of his teaching for the Social Influence MSc track, on topics of behavioral change and research methodology.