A transparent organic crystalline material guanidinium nitrate (GuN) was fruitfully harvested. Structure of GuN was verified by SXRD and its monoclinic system with Cm space group. Optical nature of GuN was confirmed by T%, n, ∆n and optical limiting. Strength nature of the GuN was tested by optical and mechanical hardness. The energy gap, global reactivity descriptors, linear and non-linear optical parameters were calculated at B3LYP/6-31G (d,p) level. Second- and third-order effective non-linearity was deliberated experimentally. © 2021, The Author(s), under exclusive licence to Springer Science+Business Media, LLC part of Springer Nature.