Two novel complexes [Zn(L)₂·(NO₃)₂] (1) and [Ni(L)₂·2H₂O]·2CH₃OH·(NO₃)₂ (2) (L = 2-(2-thiazolyl)-4-methyl-1,2-dihydroquinazoline-N³-oxide) were synthesized successfully and characterized by elemental analysis, as well as various spectroscopic techniques. Specifically, the photoluminescence behavior of complex 1 was explored in different solvents. The structural characterization of both complexes has been determined single-crystal X-ray diffraction. It revealed that the metals in 1 and 2 are chelated by two L ligands in centro-symmetrically fashion and the complexes are counterbalanced by nitrate ions which act as coordinating species in 1, while two water molecules complete the Ni coordination sphere in 2. In the crystal structures, the adjacent molecules of complex 1 disclosed a ladder-like 2-D network and 3-D supramolecular self-assembly. Simultaneously, an infinite 1-D chain, 2-D layered skeleton, and even meter-shaped 3-D network of 2 was governed by molecular interactions (H–bonds, C–H⋯π). Most strikingly, the research of antibacterial activity proved that two complexes had good activity against two standard bacteria strains. To ascertain deeply the optimum geometric configurations and detect the frontier molecular orbital energy gaps, density functional theory (DFT) calculations were also investigated. Additionally, analyses of Hirshfeld surfaces (HS) and electrostatic potential (ESP) were also performed to quantify the presence of diverse noncovalent interactions.