High resolution and fast detection of molecular vibrational absorption is important for organic synthesis, pharmaceutical processes, and environmental monitoring, and is enabled by mid-infrared (mid-IR) laser frequency combs via dual-comb spectroscopy. Here, we demonstrate a novel and highly simplified approach to broadband mid-IR dual-comb spectroscopy via supercontinuum generation, achieved using unprecedented nanophotonic dispersion engineering that allows for ultra-broadband and flat-envelope mid-IR frequency combs. Our mid-IR dual-comb spectrometer has an instantaneous bandwidth covering the functional group region from 2800–3600cm−1, comprising more than 100,000 comb lines, enabling parallel gas-phase detection with a high sensitivity, sub-Doppler spectral resolution, and a high speed. In addition to the traditional functional groups, their isotopologues are also resolved in this supercontinuum-based dual-comb spectroscopy. Our approach combines well established fiber laser combs, digital coherent data averaging, and integrated nonlinear photonics, each in itself a state-of-the-art technology, signaling the emergence of mid-IR dual-comb spectroscopy for use outside of the protected laboratory environment.