In this study, we unveil a novel perovskite compound, Na_1/3Sr_1/3Tb_1/3Cu₃Ti₄O₁₂, synthesized through a solid-state reaction method, exhibiting remarkable giant dielectric response, nonlinear characteristics, and humidity sensing capabilities. This research highlights the emergence of a Cu-rich phase, the properties of which undergo significant alterations depending on the sintering conditions. The optimization of sintering parameters, encompassing a temperature range of 1040–1450 °C for 1–8 h, resulted in substantial dielectric permittivity (ε′) values (∼2800–6000). The temperature dependence of ε′ demonstrated relationship to the particular sintering conditions utilized. The acquired loss tangent values were situated within encouraging values, ranging from 0.06 to 0.16 at 1 kHz. Furthermore, the material revealed distinct nonlinear electrical characteristics at 25 °C, with the nonlinear coefficient values of 5–127, depending on ceramic microstructures. Additionally, we delved deeply into the humidity-sensing properties of the Na_1/3Sr_1/3Tb_1/3Cu₃Ti₄O₁₂ material, showing a considerable variation in ε′ in response to fluctuations in relative humidity, thereby indicating its prospective application in humidity sensing technologies. The hysteresis error and response/recovery times were calculated, highlighting the versatility of this compound and its promising potential across multiple applications. The Na_1/3Sr_1/3Tb_1/3Cu₃Ti₄O₁₂ not only shows remarkable giant dielectric responses but also portrays significant promise for nonlinear and humidity sensing applications, marking it as a significant participant in the advancement of perovskite-based functional materials.