Ernst trained in Internal Medicine and Gastroenterology. He became professor of Medicine and chair of the Departments of Gastroenterology and Hepatology (2000), Internal Medicine (2006), and Surgery (2012) of Erasmus MC University Medical Center in Rotterdam, the Netherlands. His clinical and research interests included early neoplastic gastrointestinal conditions, and colorectal cancer screening. He is fellow of the American Gastroenterology Association and the World Endoscopy Organization’s regional lead on colorectal cancer screening for Europe and the Middle East. He organized and contributed to various international guidelines on cancer screening. He serves since 2013 as CEO of Erasmus MC, a university medical institute that includes a medical school, research facilities and hospitals. It has 4.500 biomedical students, 17.000 employees and an annual budget of 1.7 billion euro. It is the largest university medical center in the Netherlands. In addition, he chaired the board of the Dutch Federation of University Medical Centers, a group of 8 UMCs with 67.000 employees. He also chairs the Dutch national emergency medicine network, and is member of the Dutch national committee for capacity planning of medical specialists and the Dutch National Health Council.