<p>With the increasing demand for seismic resistance in high-rise and long-span structures, conventional buckling-restrained braces (BRB) face limitations such as a single energy dissipation mechanism. This study proposes a novel buckling-restrained brace featuring a negative Poisson’s ratio (NPR) effect and a spindle-shaped truss restraint. A finite element model of the BRB was developed, and its elastoplastic bearing capacity and hysteretic behavior were investigated using finite element software. A design method based on the threshold constraint ratio of the energy-dissipative BRB was proposed. The elastic buckling performance of the brace was examined, yielding a theoretical formula for the elastic buckling load and an expression for its constraint ratio. Variations in the constraint ratio were used to analyze the elastoplastic bearing capacity under monotonic axial compression and the hysteretic behavior under cyclic loading, investigating the brace’s instability modes, ultimate load capacity, and energy dissipation performance. The threshold constraint ratio of the brace was determined, providing a basis and methodology for the design of this innovative BRB. Results demonstrate that the unique mechanical properties of the NPR structure, particularly its anomalous lateral expansion under axial compression, create a self-reinforcing radial restraint mechanism, effectively suppressing local buckling tendencies observed in conventional braces. The integrated design eliminates slippage issues inherent in traditional decoupled systems, enabling the truss restraint to respond in real time to core deformation. The spatial truss effect of the spindle-shaped components ensures uniform three-dimensional stress distribution, with a threshold constraint ratio of 3.82 for the energy-dissipative brace.</p>