He is director of the Mycology Reference Laboratory and board member of the Center of Expertise in Mycology Radboudumc/CWZ. This Center of Expertise aims to improve the diagnosis and management of fungal diseases. Training courses are an important focus to increase the interest and capacity of health care workers in the field of fungal diseases.

His research interests include the diagnosis and treatment of invasive fungal diseases, focusing on aspergillosis and other invasive mold diseases. Recently he has worked on triazole resistance in Aspergillus species. To facilitate epidemiological research in the area of triazole resistance, together with colleagues he set up the ECMM/ISHAM working group on Aspergillus Resistance Surveillance. Professor Verweij is chair of the Netherlands Society for Medical Mycology and secretary of the Infectious Diseases Group of the EORTC.