The performance, combustion, and emission parameters of a thermal barrier-coated (TBC) compression ignition (CI) engine were experimentally examined using biohythane (biohydrogen + biomethane) as leading fuel and diesel as secondary fuel. The mixture of supplied fuel was blended with 85–95% biomethane and 5–15% biohydrogen, mixed with the inlet air, and supplied through the intake manifold for both coated and uncoated conditions. Yttria-stabilized zirconia with a thickness of 0.4 mm was used as the top coat on the valves and piston crown over 0.1 mm thickness NiCrAlY bond coat using the plasma spray method. Baseline data were obtained by running the engine with conventional diesel fuel, and the same was compared with dual-fuel operation at constant engine speed and variable loading conditions. Results indicated that 15% biohydrogen enrichment with TBC operation improved the engine brake thermal efficiency (BTE) by 6% compared to diesel-only mode. Further, peak cylinder pressure and heat release rate were improved up to 16.5–20% with TBC and biohythane under dual-fuel mode compared to diesel-only mode. Moreover, the emission characteristics such as hydrocarbon (HC), carbon monoxide (CO), and smoke were reduced up to 16.2, 29.1, and 62.6%, respectively, with TBC and biohythane compared to the base diesel operation owing to low carbon concentration and improved combustion characteristics.