This study highlights the potential of Sesbania grandiflora (Sesban flower) extract (SFE) as a sustainable, plant-based ingredient to enhance the functional and preservation qualities of gel-based foods. By incorporating SFE at varying concentrations (1%, 3%, and 5%) into jelly formulations and evaluating their performance over 30 days of refrigerated storage at 4°C, the research aimed to develop cleaner-label, naturally preserved alternatives to conventional additives. The 5% SFE jelly demonstrated the highest levels of bioactive compounds, including total phenolics (9.63 ± 0.29 mg GAE/g dw) and flavonoids (5.27 ± 0.28 mg QE/g dw), as well as significantly improved antioxidant activity (DPPH: 14.04 ± 0.20 μM Trolox/g dw; FRAP: 8.81 ± 1.53 μM Trolox/g dw), far exceeding the control. In addition to functional benefits, the SFE-enriched jellies exhibited reduced hardness while maintaining desirable texture characteristics. Notably, the 3% and 5% SFE formulations inhibited microbial growth throughout the 30-day storage period, effectively prolonging shelf life without synthetic preservatives. The visual change in jelly coloration (ΔE = 11.29 ± 0.52 at day 30) also indicated SFE’s natural pigmentation potential. These results underscore the multifunctionality of SFE as a natural, renewable ingredient that supports food safety, extends product longevity, and minimizes environmental and health concerns associated with artificial additives. This approach contributes to the broader goal of advancing sustainable food systems by utilizing underexploited botanical resources in value-added food product development.