This study investigated the self-sensing mechanism in the electromagnetic vibration-based energy harvester (EV-EH) prototype specially engineered for a commercial magnetorheological (MR) damper. The objective of the work is to demonstrate that the EV-EH unit with a specific self-powered feature can also be employed as a relative velocity sensor in the system. To do this, the self-sensing action of the unit was experimentally studied over the assumed range of working conditions. The analysis of the test results and the determined self-sensing function indicated that the EV-EH has a highly accurate monitoring capability. The EV-EH self-sensing and self-powered features confirm the potentials and applicability of the unit for MR damper control in a vibration reduction system with energy regeneration.