Witness is a Public Health Specialist (FRSPH) and Cancer Epidemiologist with an interest in HIV/AIDS and sexual reproductive health. He works at the Centre for Health Policy, School of Public Health, the University of Witwatersrand as a Health Systems and Policy Researcher. As a Health Systems and Policy Researcher, Witness engages with policymakers, decision-makers and health practitioners on their need and use of evidence in their day-to-day activities. He is a Fellow of the Royal Society for Public Health, and a member of both the International Society for Infectious Diseases and International Epidemiological Association. He is involved in pushing the agenda for open science practices in public health and medicine through evidence systematic maps, systematic reviews and meta-analysis.