Considerable attention has recently been paid to the consumer demand for healthy, fortified, and vegan products. Moreover, there has been increasing interest in the reuse of food processing by-products in order to reduce the environmental impact and simultaneously valorize waste through its conversion into value-added products. In the present study, the appropriate degree of grinding the pomace from yellow watermelon cv. Janosik was based primarily selected based on the water-binding capacity (WBC) and cation exchange capacity, as these parameters are indicative of the pomace’s functionality in food applications. Next, the basic chemical composition of powdered pomace, i.e. the content of fiber, fat, protein, vitamin C, total phenolic compounds, flavonoids, and anthocyanins and antioxidant activity, were determined. The next stage of the study consisted in preparation of jelly candies supplemented with different concentrations of powdered pomace (20, 35, and 50%), citric acid (0.75 and 1%), and agar (0.5 and 1%) and assessment of their physicochemical and textural properties. The pomace was obtained from whole yellow watermelon fruits (cv. “Janosik”) that were pressed without prior peeling, meaning the material included both the edible flesh and parts of the rind. The results showed that the increase in the concentration of the powdered additive was accompanied by a decrease in the moisture content and water activity of the jellies and an increase in their pH value. Additionally, the jellies became lighter and more yellowish, as indicated by increasing values of the L* and b* parameters. In turn, textural analysis showed a significant (p < 0.05) increase in hardness, gumminess, and chewiness of the jellies with increasing concentrations of powdered pomace, citric acid, and agar. For example, hardness increased from 1598 N in the lowest supplementation (sample JC1) to 6984 N in the highest (sample JC12), gumminess from 904 to 2697 g, and chewiness from 41.7 to 122.6 N mm.