The IT Service Management (ITSM) industry has defined processes as best practices in the widely-accepted IT Infrastructure Library (ITIL) framework. However, studies on the measurement of ITSM process improvement are scant. Our research addressed the dual problems of the lack of transparency and the need for efficiency in ITSM process assessment. Using the Design Science Research methodology, we developed a Software-mediated Process Assessment (SMPA) approach that enables assessment of ITSM processes. The SMPA approach includes process selection; an online survey to collect assessment data; measurement of process capability; and reporting of process improvement recommendations. We implemented a decision support system (DSS) to automate the SMPA approach and evaluated it at two IT service providers. The evaluations indicated that the SMPA approach supports decision-making on process improvements. The findings provided design knowledge of virtualisation in ITSM process assessment and how this may facilitate continual service improvement.