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Nearly 57 Mt of food waste are generated annually in the EU for many reasons, for instance, because of microbial food spoilage. So, actions to reduce food loss and waste are needed and active packaging could offer a new approach towards this aim. In this study, antimicrobial gelatin films were prepared via the solution casting technique and their physicochemical, optical, mechanical, structural, barrier and antimicrobial properties were analysed. First, gelatin films were photo-crosslinked with riboflavin and the photo-curation time (0–4 h) was optimized. The optimal crosslinking time was 2 h since the solubility dropped down from 100% to 30% after 2 or 4 h of UV exposure. Then, 2 types of chitin nanowhiskers (CNWs) obtained via acid hydrolysis (AH) and TEMPO-mediated oxidation processes were added in 2 concentrations (2 and 4 wt %) into the film-forming solution (FFS) as reinforcements before film photo-crosslinking. The AH-CNW at 4 wt % was chosen as an optimal CNW type and concentration because they further decreased the solubility (∼24%) of films and improved mechanical properties up to values similar to those of commercially available synthetic packaging films. Finally, various concentrations (0, 7.5, 15 and 30 wt %) of the antimicrobial compound (Nisin A®) were added to the optimized formulation which showed good antimicrobial properties on both spoilage and pathogen strains, as well as over the native microbiota of chilled sea bream fillets, sliced cold-smoked salmon and chicken breast fillets. The developed films displayed promising properties as antimicrobial packaging for myosistem foods.