Catalytic methane decomposition (CMD) is a promising technology for large-scale production of COx-free H2 from natural gas that can also produce valuable carbon byproducts. Although equilibrium conversions and reaction rates of CMD generally increase with temperature, operation in a low-temperature regime with simultaneous H2 recovery could potentially lead to operating cost and energy savings. Here, we report that well-dispersed Ni–SiO2, derived from high-temperature reduction of nickel phyllosilicates, is active for CMD at temperatures below 500 °C, with initial H2 production rates of up to 5.3 mol H2/gcat·h at 25% CH4 conversion. This ability to achieve rates comparable to other well-established catalysts is contrary to expectations that small (<ca. 10 nm) Ni nanoparticles are inactive for CMD because of rapid deactivation and attributed here to an unusual mobility of nickel–silica interfaces in the presence of CH4 that leads to controlled sintering of the originally well-dispersed Ni nanoparticles. We further show that the ratio of 1:1 and 2:1 nickel phyllosilicates in the precursor, which governs catalyst reducibility and can be tuned by adding NH4F to the synthesis mixture, is a key descriptor of catalytic performance. Our findings provide valuable insight into catalyst and process design for low-temperature CMD.