AgNbO₃ (AN) and modified AgNbO₃ have been extensively investigated as promising lead-free antiferroelectric (AFE) energy storage materials. Previous studies have focused mainly on the use of an ion dopant at the A/B site to obtain a stabilized AFE phase; however, simultaneous improvements in the recoverable energy storage density (W_rec) and efficiency (η) are still difficult to realize. Herein, we innovatively constructed a AgNbO₃–NaNbO₃–(Sr_0.7Bi_0.2)TiO₃ (AN–NN–SBT) ternary solid solution to achieve a relaxor AFE in AgNbO₃-based materials. The coexistence of antiferroelectric (M₃) and paraelectric (O) phases in 0.8(0.7AgNbO₃–0.3NaNbO₃)–0.2(Sr_0.7Bi_0.2)TiO₃ confirms the successful realization of a relaxor AFE, attributed to multiple ion occupation at the A/B sites. Consequently, a high W_rec of 7.53 J·cm⁻³ and η of 74.0% are acquired, together with superior stability against various temperatures, frequencies, and cycling numbers. Furthermore, a high power density (298.7 MW·cm⁻³) and fast discharge speed (41.4 ns) are also demonstrated for the AgNbO₃-based relaxor AFE. This work presents a promising energy storage AgNbO₃-based ternary solid solution and proposes a novel strategy for AgNbO₃-based energy storage via the design of relaxor AFE materials.