Gelatin as a biodegradable, biocompatible, non-toxic, non-carcinogenetic, non-immunogenic, inexpensive natural polymeric derivatives of proteins and peptides was implemented as an eco-friendly and efficient biosorbent for removal of Cr(III)–Cr(VI). A deeper understanding of the behavior and validity of gelatin as a biosorbent for interaction with Cr(III)–Cr(VI) was established. The efficient sorption properties of gelatin for Cr(III)–Cr(VI) was confirmed by metal capacity determination. Biosorption equilibria and mechanisms were examined and evaluated by using various isotherm models. The potential applications of gelatin for biosorption and removal of Cr(III)–Cr(VI) from real water samples were successfully accomplished (∼97.5–102.0±2.5–4.0%).