<p>The thermoelectric properties of co-doping Fe₂CrAl_{1−2<i>x</i>}Ni_<i>x</i>Sn_<i>x</i> (<i>x</i> = 0, 0.05, 0.1, 0.2) Heusler alloys were systematically investigated through combined experimental characterization and first-principles calculations to understand the structure–property relationships governing transport performance. Density functional theory calculations reveal a dramatic 17-fold enhancement in density of states near the Fermi level, increasing from 2–3 states/eV for the parent Fe₂CrAl to 52 states/eV with Ni–Sn substitution, providing fundamental insights into the electronic structure modifications. X-ray diffraction analysis demonstrates systematic phase evolution with composition, where <i>x</i> = 0.1 exhibits coherent Ni₃Sn₂ precipitates. Temperature-dependent electrical resistivity measurements from 300–700&#xa0;K reveal thermally activated conduction above 550&#xa0;K, with energy gap analysis showing non-monotonic behavior and a maximum energy gap of 12.2&#xa0;meV at <i>x</i> = 0.1. This enhanced energy gap effectively suppresses bipolar conduction effects at elevated temperatures, extending the useful operating range for thermoelectric applications. Thermal conductivity measurements indicate optimal phonon scattering at <i>x</i> = 0.1, where lattice thermal conductivity reaches a minimum of 5.03&#xa0;Wm⁻¹&#xa0;K⁻¹ at 300&#xa0;K. The synergistic combination of enhanced electronic properties through secondary phase formation and reduced thermal conductivity results in an 882% relative improvement in thermoelectric figure of merit compared to the parent Fe₂CrAl compound, reaching an absolute ZT value of 1.67 × 10⁻³ for the x = 0.1 composition at 700&#xa0;K. While this represents significant progress in Fe₂CrAl-based materials, the absolute ZT remains modest compared to state-of-the-art Heusler thermoelectrics such as Fe₂VAl (ZT ~ 0.5) and requires further optimization for practical applications.</p>