Abstract <p>Single crystals of the <i>n</i>-type type-VIII clathrate Ba₈Ga_{16–<i>x</i>}Ag_<i>x</i>Sn₃₀ (<i>x</i> = 0, 0.5, 1) were synthesized using the Sn-flux method. Elemental analysis reveals an extremely low actual Ag incorporation (<i>x</i>_real ≈ 0.034–0.037) despite much higher nominal compositions. From a theoretical standpoint, the structural and electronic properties of the Ag-substituted type-VIII clathrate Ba₈Ga_{16–<i>x</i>}Ag_<i>x</i>Sn₃₀ were systematically investigated using first-principles calculations. All samples exhibited negative Seebeck coefficients across the measured temperature range, confirming their <i>n</i>-type conduction. However, the results derived from theoretical calculations indicated that all samples displayed <i>p</i>-type conduction behavior. The interesting discrepancy between the experimental and computational results is attributed to variations in the ratio of framework atoms. Detailed analysis confirmed that these clathrates are indirect bandgap semiconductors, with the bandgap widening as the Ag doping concentration increases. Experimentally, the magnitude of the Seebeck coefficient for the <i>x</i> = 1 sample reached approximately 330 μV K^–1 at 600 K. Furthermore, the temperature-dependent transport properties of these clathrates are consistent with the typical behavior of heavily doped semiconductors. Consequently, the <i>x</i> = 1 sample achieved a maximum power factor of 1.49 × 10^–3 W m^–1 K^–2 at approximately 540 K. Among all synthesized Ba₈Ga_{16–<i>x</i>}Ag_<i>x</i>Sn₃₀ compounds, the <i>x</i> = 1 sample exhibited the highest thermoelectric performance across the measured temperature range, reaching an estimated maximum figure of merit of 1.2 at 600 K.</p>