A novel and facile in-situ seed-mediated synthetic approach has been developed to reduce non-noble metal precursors (Ni2+, Co2+, Fe2+, etc.) at room temperature, by taking advantage of a trace amount of noble metal cations (Ag+, Pd2+, Pt2+, Au3+, etc.) as a seed/initiator and NH3BH3 as a moderate reducing agent. The obtained noble metal-seed-mediated (NMSM) non-noble metal nanoparticles (NPs) stabilized by a metal-organic framework are low-cost and display superior catalytic activity in the hydrolytic dehydrogenation of NH3BH3 under ambient conditions. As a representative catalyst, Ag-doped Ni/MIL-101 (with Ag/Ni molar ratio as low as 1/200), exhibiting much higher activity than any other corresponding counterparts.