<p>The brass (JIS C2600) substrate was first subjected to appropriate roughening and activation pretreatment, followed by surface modification via electroless plating, including the deposition of Ni–P and Ni–P-Co coatings, along with the application of an external magnetic field. The Taguchi method (L₉ 3⁴) was employed to optimize the key input variables of the process—specifically bath temperature, deposition time, pH value, and NiSO₄ concentration—to study their effects on the microstructure, mechanical properties, fatigue life, and miniature-journal bearings’ wear. The Ni–P coating exhibits a broad diffraction peak at 2θ ≈ 44.51°, indicating that it is mainly amorphous or has low crystallinity. The appearance of the (200) peak after Co incorporation into the Ni–P matrix indicates increased crystallinity, suggesting that the structure evolves from an amorphous Ni–P phase to a nanocrystalline Ni–P-Co structure with amorphous-crystalline mixed characteristics. Regarding the main outputs and achievements, the optimized Ni–P coating effectively inhibited crack initiation, delaying the fatigue fracture from the 24th to the 54th bending cycle compared to the original substrate. Furthermore, the ternary Ni–P-Co coating, especially when assisted by a 0.18&#xa0;T external magnetic field, demonstrated superior performance. Compared to the binary Ni–P coating, the magnetic field-assisted Ni–P-Co coating achieved a 64% increase in hardness, a 50% decrease in miniature-bearing wear loss, and a 52% improvement in fatigue life.</p>