Energy harvesting from ambient vibration is an emerging and promising solution to the power supply problem associated with autonomous sensors. This article proposes a novel strategy of harvesting damping energy from vibration control devices. A novel system, termed electromagnetic damper cum energy harvester, is employed to fulfill both vibration damping and energy harvesting functions. Electromagnetic damper cum energy harvester is essentially an electromagnetic device connected to a specially designed energy harvesting circuit, which is a buck–boost converter operating in a discontinuous conduction mode. The energy harvesting circuit can achieve satisfactory efficiency without any feedback loop. The effectiveness of the dual-function electromagnetic damper cum energy harvester is demonstrated through a numerical case study of bridge stay cables under wind excitations, in which the major parameters of electromagnetic damper cum energy harvester are determined through a simple design approach. Simulation results project average output power ranging from 82.5 to 2396.8 mW at a wind speed of 9–15 m/s, corresponding to an overall efficiency of 42.3%. The dual-function electromagnetic damper cum energy harvester also exhibits vibration control performance comparable to an optimally designed viscous fluid damper.