Onychomycosis also referred to as dermatophytic onychomycosis or Tinea unguium, is a fungal nail infection primarily caused by dermatophytes (like Trichophyton rubrum), yeasts (like Candida albicans), and non-dermatophytic moulds. In this study, an effort was made to develop a herbal medicated antifungal nail lacquer using Caesalpinia bonducella seeds. The objective was to enhance clinical efficacy while improving patient compliance. Authenticated C. bonducella seeds were extracted and formulated into nail lacquers using suitable excipients, including film-forming agents, plasticizers, solvents, penetration enhancers, and resins. The prepared formulations were evaluated for various physicochemical and biological parameters such as smoothness, glossiness, non-volatile content, drug content, adhesion, diffusion, and antifungal activity (zone of inhibition). FTIR analysis confirmed drug–excipient compatibility by retaining characteristic peaks. Among the formulations, F5 was identified as the optimized batch and subjected to accelerated stability testing under ICH guidelines at 37 ± 2 °C for one month. The results showed no significant changes in its initial characteristics, while the formulation maintained excellent antifungal activity. Overall, the developed antifungal nail lacquer demonstrated safety, stability, and effectiveness, suggesting its potential as a novel dosage form for the treatment of dermatophytic nail infections such as onychomycosis. Its use may significantly improve therapeutic outcomes and patient adherence compared to conventional therapies.