Multinary intermetallic compounds with rich chemical compositions enable one to achieve a logical design for desired materials based on the required function. In this work, we have demonstrated a step-by-step strategy to design a quaternary intermetallic compound that exhibits highly active and stable performance for the hydrogen evolution reaction (HER). With binary intermetallic TaCo 2 as the starting point, the minor inclusion of a ductile Cu element in TaCo 2 to form ternary TaCu 0.25 Co 1.75 can substantially lower the degradation rate from ca. 20% to 5% after sintering treatment ( i.e. , enhance connectivity between particles). However, the overpotential at a current density of 10 mA cm −2 ( η 10 ) increases by ca. 20 mV from TaCo 2 to TaCu 0.25 Co 1.75 . Further incorporation of a HER active Ru element to cast quaternary TaCu 0.125 Ru 0.125 Co 1.75 can decrease ca. 70 mV of η 10 while maintaining long-term stability. This proves that one can design functional intermetallic compounds intentionally, which may be extended to different fields of application. Multinary intermetallic compounds with rich chemical compositions enable one to achieve a logical design for desired materials based on the required function.