AbstractConsiderable effort has been invested in the development of non‐centrosymmetric (NCS) inorganic solids for ferroelectricity‐, piezoelectricity‐ and, particularly, optical nonlinearity‐related applications. While great progress has been made, a persistent problem is the difficulty in constructing NCS materials, which probably stems from non‐directionality and unsaturation of the ionic bonds between metal counter‐cations and covalent anionic modules. We report herein a secondary‐bond‐driven approach that circumvents the cancellation of dipole moments between adjacent anionic modules that has plagued second‐harmonic generation (SHG) material design, and which thereby affords a polar structure with strong SHG properties. The resultant first NCS counter‐cation‐free iodate, VO2(H2O)(IO3) (VIO), a new class of iodate, crystallizes in a polar lattice with VO2(H2O)(IO3)] zigzag chains connected by weak hydrogen bonds and intermolecular forces. VIO exhibits very large SHG responses (18 × KH2PO4 @ 1200 nm, 1.5 × KTiOPO4 @ 2100 nm) and sufficient birefringence (0.184 @ 546 nm). Calculations and crystal structure analysis attribute the large SHG responses to consistent polarization orientations of the VO2(H2O)(IO3)] chains controlled by secondary bonds. This study highlights the advantages of manipulating the secondary bonds in inorganic solids to control NCS structure and optical nonlinearity, affording a new perspective in the development of high‐performance NLO materials.