Sam has been a journalist since 1986. He has worked for the investigative magazine noseweek, served as political editor of the Sunday Tribune, and joined the Mail & Guardian as investigative journalist in 2002. In 2003 he won the Vodacom Journalist of the Year award for first reporting the criminal investigation of then national deputy president Jacob Zuma.

Together with colleague Stefaans Brümmer he has received numerous journalism awards, including for their Oilgate exposés that traced the involvement of an ANC-linked company in diverting money from a state contract to the coffers of the ruling party. Sam was instrumental in revealing the links between former police commissioner Jackie Selebi, slain mining magnate Brett Kebble and various figures from South Africa's underworld, including Glenn Agliotti. Together with Stefaans and Adriaan Basson, Sam won the Taco Kuiper award in 2009 for sustained investigation of the notorious South African arms deal.

Sam co-founded amaBhungane in 2010.