A new noncentrosymmetric pyrophosphate, LiGaP2O7, is designed and synthesized by a reasonable energy-band regulation engineering strategy with isovalent substitution. The title compound crystallizes in the monoclinic space group P2(1) (No. 4) with lattice parameters a = 4.7593(10) angstrom, b = 7.9586(16) angstrom, c = 6.8940(14) angstrom, and Z = 2, which is the isomorphic compound of LiMP2O7 (M = Fe, Cr). Compared with LiMP2O7, LiGaP2O7 exhibits a wide band gap of 4.56 eV due to no d-d electronic transitions. Meanwhile, good phase-matching ability and a moderate second-harmonic generation (SHG) response in LiGaP2O7 are maintained. First-principles calculations of the band structure and nonlinear-optical performance were also performed in order to gain insight into the role of the Ga-O groups in the band gap and SHG effect source.