Hydrogen as a source of clean and future alternative to fossil fuels demands a class of powerful gas sensor technologies. To this end, we have developed unique bi-stacked heterogeneous layers based on 2D Pnictogens and graphene sheets via photolithography and pattern transfer methods. The nanoengineered heterostructure morphology consists of truncated/hexagonal antimonene flakes dispersed on graphene sheets. Amongst the Pnictogen class, the hybrid antimonene-graphenes (Sb/G) demonstrated excellent sensing behavior characterized by a large gas response to H2 (~4-fold improvement), high selectivity, fast response/recovery times (>3 fold reduction), and ultra-low limit of detection (LOD: 0.05 ppm) in comparison to pristine sensors. The microstructural and density functional theory (DFT) calculations demonstrated a Bader charge transfer mechanism from Sb/G heterojunction to the H2 gas, which modulated the Schottky barrier and improved gas response. The outstanding performance of the Sb/G sensor places it amongst the highly selective and fast hydrogen sensors based on the Pnictogen-graphene family.