We have designed and synthesized a new, highly efficient electro-optic vanillin-based quinolinium crystal. The HMQ-NS (2-(4-hydroxy-3-methoxystyryl)-1-methylquinolinium naphthalene-2-sulfonate) crystals exhibit an acentric monoclinic space group symmetry Pn with a large effective molecular hyperpolarizability in the crystal with the diagonal component β^eff₃₃₃ = 149 × 10⁻³⁰ esu, which is comparable to that of benchmark ionic stilbazolium crystals, and a good thermal stability. Therefore, the newly developed HMQ-NS crystal is an attractive candidate for nonlinear optical and electro-optic applications.