Kristof is an industrial pharmacist. Being a Belgian national, he started working for the Belgian Federal Agency of Medicines and Health Products in 2005, and in 2009 he took up the responsibility for the Research and Development division, in charge of clinical trial applications. He was the Belgian member and secretary of the Clinical Trial Facilitation Group, and the Belgian representative in the European Commissions Clinical Trial Expert Group. He was also part of the negotiations of the Clinical Trial Regulation in 2013 and 2014. After a brief period working for the association of the Belgian pharmaceutical industry from 2016 onwards, he joined the EU Commission in 2019.