Electrochemical water splitting is an environmentally friendly way of producing hydrogen, but this process requires highly efficient catalysts. Platinum (Pt) is known the best catalyst for hydrogen evolution reaction (HER) in acidic media, but the scarcity and high cost of Pt limits its applicability in widespread technologies. In this work, we have uncovered the role of underlying substrate on the HER activity of atomically dispersed Pt atoms. A DC magnetron sputtering technique has been utilized to deposit transition metal (Cu, Mo, W, Ti and Ta) thin films as underlying substrates for atomically dispersed and extremely low loading of Pt (< 1.5 at%). As synthesized samples were characterized as electrocatalysts for the HER in both alkali and acidic media. In combination of standard electrochemical experiments (e.g., CV), the differential electrochemical mass spectrometry (DEMS) results show that despite low loading of Pt, the prepared catalysts produce hydrogen at a rate comparable with that of a pristine Pt. Based on the XPS study, the excellent performance is attributed to the modified electronic properties of the Pt atoms due to interaction with underlying substrates. Additionally, the performance of the Pt atoms is significantly governed by the physical properties of underlying substances. Our catalysts also displayed good stability for HER activity and found to be stable after 1000 cycles of continuous operation.