•Hydrogen-rich syngas is generated from eucalyptus wood and corncob waste in a open top downdraft gasifier.•Evolutionary characteristics of hydrogen-rich product gas studied.•Effect of temperature and time on gasification process has been analysed.•TG-DTG-DTA biomasses and morphology analysis of char carried out. The gasification of biomass waste integrated with thermal usage and power generation is a sustainable approach to generate energy. Present work focuses on operational assessment of an open-top downdraft gasifier at different flow rates of 10.5 and 12.5 g/s using corn cob and eucalyptus wood waste as feedstocks. Gasification characteristics (performance and syngas parameters), morphological characteristics (X-ray Diffraction, Fourier Transform Infrared Spectroscopy, Scanning Electron Microscopy), and thermogravimetric analysis are performed and analysed. The results indicate that values of the lowest hydrogen and carbon monoxide mole fractions, for corncob are 10.81 and 10.11 at the equivalence ratio (ER) of 0.278 and moisture content of 10%. Whereas the highest mole fraction of hydrogen and carbon monoxide for eucalyptus in the producer gas are 14.1 and 12.58 at ER of 0.125 and moisture of 15%. The syngas obtained from eucalyptus wood waste was better in terms of hydrogen content as compared to that from corn cob feedstock as the future vies greater role for hydrogen based fuels.