Hennie works as the director of Open Secrets – a South African non-profit holding powerful private actors to account for economic crimes. He and is a past fellow of the Open Society Foundation for South Africa and Senior Research Associate at the Institute for Justice and Reconcilliation.

He has also worked as Director of the Institute for Security Studies in Cape Town and for Transparency International in Berlin. Hennie supports the Right2Know campaign and serves on the boards of Natural Justice and My Vote Counts. He is the author of Apartheid Guns & Money: A Tale of Profit (2017) and co-author of The Devil in the Detail: How the Arms Deal Changed Everything (2011).