This investigation deals with the design, manufacturing, and testing of a large-capacity MR damper prototype. The MR damper uses external coils that magnetize the MR-fluid as it moves out of the main cylinder through an external cylindrical gap. In its design, multi-physics numerical simulations are used to better understand its force–velocity constitutive behavior, and its eventual use in conjunction with tuned mass dampers for vibration reduction of high-rise buildings. Multi-physics finite element models are used to investigate the coupled magnetic and fluid-dynamic behavior of these dampers and thus facilitate the proof-of-concept testing of several new designs. In these models, the magnetic field and the dynamic behavior of the fluid are represented through the well-known Maxwell and Navier–Stokes equations. Both fields are coupled through the viscosity of the magneto-rheological fluid used, which in turn depends on the magnetic field strength. Some parameters of the numerical model are adjusted using cyclic and hybrid testing results on a 15 ton MR damper with internal coils. Numerical and experimental results for the 15 ton MR damper showed very good agreement, which supports the use of the proposed cascade magnetic-fluid model. The construction of the 97 ton MR damper involved several technical challenges, such as the use of a bimetallic cylinder for the external coils to confine the magnetic field within a predefined magnetic circuit. As it should be expected, test results of the manufactured MR damper show that the damping force increases with the applied current intensity. However, a larger discrepancy between the predicted and measured force in the large damper is observed, which is studied and discussed further herein.