It is crucial to discover lead-free materials with ultrahigh recoverable energy density ($W$${}_{\mathrm{rec}}$) that can be employed in future pulse power capacitors. In this work, a high$W$${}_{\mathrm{rec}}$of 4.51 J/cm³ was successfully obtained in lead-free Nd-doped AgNb${}_{0.8}$Ta${}_{0.2}$O₃ antiferroelectric ceramics at an applied electric field of 290 kV/cm. It is discovered that Nd doping paired with Nb-site vacancies could stabilize the antiferroelectric phase by lowering the temperatures of the M1–M2 and M2–M3 phase transitions, which leads to higher energy storage efficiency. Furthermore, Nd and Ta co-doping will contribute to the electrical homogeneity and low electrical conductivity, resulting in large breakdown strengths. Aliovalent doping in Ag-site with Nb-site vacancies serves as a novel strategy for the construction of AgNbO₃-based ceramics with excellent energy storage performance.It is crucial to discover lead-free materials with ultrahigh recoverable energy density ($W$${}_{\mathrm{rec}}$) that can be employed in future pulse power capacitors. In this work, a high$W$${}_{\mathrm{rec}}$of 4.51 J/cm³ was successfully obtained in lead-free Nd-doped AgNb${}_{0.8}$Ta${}_{0.2}$O₃ antiferroelectric ceramics at an applied electric field of 290 kV/cm. It is discovered that Nd doping paired with Nb-site vacancies could stabilize the antiferroelectric phase by lowering the temperatures of the M1–M2 and M2–M3 phase transitions, which leads to higher energy storage efficiency. Furthermore, Nd and Ta co-doping will contribute to the electrical homogeneity and low electrical conductivity, resulting in large breakdown strengths. Aliovalent doping in Ag-site with Nb-site vacancies serves as a novel strategy for the construction of AgNbO₃-based ceramics with excellent energy storage performance.