Low-cost and highly active catalysts are attractive for catalysing formic acid (FA) dehydrogenation at room temperature. The PtNi alloy nanoparticles with the characteristic of lattice contraction and synergy effects were loaded on two-dimensional TiB₂ by incipient-wetness impregnation. Compared to Pt/TiB₂, the substitution of Ni reduces the amount of noble metal required, with the added advantage of significantly improving the catalyst activity by sixteen times. By investigating the various PtNi ratios, the Pt₃Ni₈/TiB₂ (total metal loading = 2.0 wt%) catalyst was found to provide a low activation energy of 27.7 kJ mol⁻¹ in 10.0 M FA aqueous solution at room temperature. This is the first example of using the alloy supported on TiB₂ to achieve strong metal–support interaction (SMSI) to catalyse formic acid dehydrogenation at ambient temperature. XPS and TEM characterisation studies show that higher temperatures induced TiB₂ to encapsulate the PtNi NPs, with the TiB₂ surfaces serving as the active site for catalysing FA dehydrogenation. The catalytic activity of the obtained Pt₃Ni₈/TiB₂ catalyst for the dehydrogenation of FA was much higher than those of its monometallic counterparts (Pt/TiB₂ and Ni/TiB₂) prepared by the same method, while demonstrating higher stability against agglomeration and CO poisoning. The excellent catalytic activity and stability of Pt₃Ni₈/TiB₂ were mainly attributed to the presence of the SMSI effect of the catalyst. Additionally, the lattice distortion and local interactions within the ferromagnetic clusters of Pt₃Ni₈ alloy NPs created a synergistic effect, which resulted in an enhanced SMSI effect throughout the catalyst. This study introduces a new concept that magnetic Ni metal partially replacing noble metals can improve thermal stability and catalytic performance, while enabling facile catalyst recovery. Moreover, this research demonstrates that the controlled synthesis and rational design of 2D reticular crystal structure TiB₂-supported alloy NPs may provide new opportunities to enhance the catalytic activity and improve the SMSI effect of noble metal-based nanostructures.