The increasing environmental and health concerns associated with synthetic pigments have intensified the search for sustainable and biologically derived alternatives. Actinomycetes are recognized as promising producers of natural pigments; however, pigment production by rare actinomycete genera remains underexplored. In the present study, a pigment-producing actinomycete isolated from mangrove sediment was identified as Pseudonocardia alni based on morphological, biochemical, and 16S rRNA gene sequence analyses (GenBank accession no. PP296388). Pigment production was optimized by evaluating physicochemical parameters including pH, temperature, and salinity. The feasibility of agro-waste substrates for cost-effective pigment production was assessed through solid-state fermentation. Among the tested substrates, tapioca peel supported the highest pigment yield (1.388 ± 0.034), followed by groundnut oil cake and coconut oil cake, with statistically significant differences among substrates (p < 0.05). The extracted pigment exhibited a characteristic visible absorption maximum in UV–Visible spectroscopy, indicating a conjugated chromophore, while FTIR analysis revealed aromatic, hydroxyl, carbonyl, and nitrogen-containing functional groups. The pigment showed broad-spectrum antibacterial activity against selected Gram-positive and Gram-negative pathogens. Overall, the study demonstrates the potential of Pseudonocardia alni as a sustainable source of a bioactive pigment and highlights agro-waste valorization as an effective strategy for eco-friendly pigment production.