Graphene-based electronic textile (e-textile) gas sensors have been developed for detecting hazardous NO₂ gas. For the e-textile gas sensor, electrical conductivity is a critical factor because it directly affects its sensitivity. To obtain a highly conductive e-textile, biomolecules have been used for gluing the graphene to the textile surface, though there remain areas to improve, such as poor conductivity and flexibility. Herein, we have developed a dopamine–graphene hybrid electronic textile yarn (DGY) where the dopamine is used as a bio-inspired adhesive to attach graphene to the surface of yarns. The DGY shows improved electrical conductivity (∼40 times) compared to conventional graphene-based e-textile yarns with no glue. Moreover, it exhibited improved sensing performance in terms of short response time (∼2 min), high sensitivity (0.02 μA/ppm), and selectivity toward NO₂. The mechanical flexibility and durability of the DGY were examined through a 1000-cycle bending test. For a practical application, the DGY was attempted to detect the NO_x emitted from vehicles, including gasoline, diesel, and fuel cell electric vehicles. Our results demonstrated that the DGYs—as a graphene-based e-textile gas sensor for detecting NO₂—are simple to fabricate, cheap, disposable, and mechanically stable.