We report on the thermoelectric (TE) performance of intrinsic n-type AgBiSe2, a Pb-free material with more earth-abundant and cheaper elements than intrinsic p-type homologous AgSbTe2. Pb doping changes n-type AgBiSe2 to p-type but leads to poor electrical transport properties. Nb doping enhances the TE properties of n-type AgBiSe2 by increasing the carrier concentration. As a result of the intrinsically low thermal conductivity (0.7 W m(-1) K(-1)), low electrical resistivity (5.2 mΩ cm), and high absolute Seebeck coefficient (-218 μV/K), the TE figure of merit (ZT) at 773 K is significantly increased from 0.5 for solid-state-synthesized pristine AgBiSe2 to 1 for Ag0.96Nb0.04BiSe2, which makes it a promising n-type candidate for medium-temperature TE applications.