Pertinent existing hydrogen technologies for energy storage require unsustainable amounts of scarce platinum group metals. Here, an electrocatalyst comprising high-aspect-ratio platinum nanowires (PtNWs) on single-walled carbon nanotubes (SWNTs) with ultralow Pt content (340 ngPt cm−2) is employed for hydrogen evolution reaction (HER). A comparable activity (10 mA cm−2 at −18 mV vs. RHE) to that of state-of-the-art Pt/C (38,000 ngPt cm−2) is reached in acidic aqueous electrolyte. This is attributed to favorable PtNW interaction with SWNTs and PtNW edge-sites which adsorb hydrogen optimally and aid at alleviating repulsive interactions. Moreover, the metallic nature of Pt, morphological effects and enhanced wetting contribute positively. The PtNW/SWNT relevance is emphasized at a proton-exchange-membrane electrolyzer generating stable voltage for more than 2000 h, successfully competing with the state-of-the-art reference but with one tenth of Pt mass loading. Overall, this work presents an unprecedently efficient HER catalyst and opens up avenues for PtNW/SWNT catalyzing other high-impact reactions.