Colossal dielectric materials with high permittivity and low loss are urgently demanded for modern electronic devices, yet conventional systems often suffer from high loss, poor thermal stability, or complex processing. TiO₂-based ceramics, when properly co-doped with aliovalent ions, offer a promising platform for achieving giant permittivity through defect engineering. In this study, we investigate the combinatory effects of trivalent scandium (Sc³⁺) and pentavalent vanadium (V⁵⁺) co-doping on the dielectric behavior of TiO₂ ceramics. A series of (Sc_0.5V_0.5)_xTi_1–xO₂ (SVTO-x) with x = 0.05, 0.10, 0.15, and 0.20 were synthesized via a conventional solid-state reaction method. Phase purity and crystal structure were examined by X-ray diffraction with Rietveld refinement. The analysis confirmed the formation of single-phase rutile solid solutions for x ≤ 0.15, while a minor secondary ScVO₄ phase emerged at x = 0.20. Scanning electron microscopy revealed highly dense microstructures with clear grain boundaries. The average grain size increased from ~19.4 μm (x = 0.05) to ~25.4 μm (x = 0.15), then slightly decreased at x = 0.20 owing to Zener pinning by the secondary phase at grain boundaries. Dielectric measurements revealed that the SVTO-0.05 ceramic exhibited an exceptional combination of dielectric properties: a relative permittivity (ε′) of approximately 3.9 × 10⁴ and a low dielectric loss tangent (tanδ) of ~0.0128, both measured at 1 kHz and room temperature, accompanied by outstanding frequency and thermal stability. Both ε′ and tanδ increased with temperature, indicating thermally activated polarization processes. Electric modulus spectroscopy showed two relaxation peaks, attributed to grain-boundary and bulk contributions, with activation energies of ~0.11 eV and ~0.16 eV, respectively. X-ray photoelectron spectroscopy confirmed the coexistence of Sc³⁺, V⁵⁺, Ti³⁺, and oxygen vacancies, supporting the formation of triangular and rhombic defect clusters that pin free electrons and suppress long-range conduction while preserving local dipole reorientation. The synergistic interplay between electron-pinned defect dipoles and the internal barrier layer capacitance effect is identified as the key mechanism responsible for the observed colossal permittivity and low loss. These findings demonstrate that strategic (Sc,V) co-doping constitutes an effective defect-engineering approach for designing high-performance dielectric ceramics.