The textile dyeing industry is recognized as one of the most polluting industries globally, with significant contributions to water pollution. The use of complex dyes and carcinogenic chemicals in dyeing processes hinders the natural decomposition of waste and amplifies its harmful environmental impact. Employing natural dyes from various sources presents more sustainable alternative for textile dyeing. However, the main drawbacks of natural dyes are their dull colours and poor wash fastness. In contrast, algae are capable of naturally producing vibrant colours, prompting efforts to explore algae-based pigments for textile dyeing. In this research, phycocyanin extracted from Spirulina platensis algae was used to dye cellulosic fabrics. Various mordants, including cream of tartar, alum, tannic acid, and ferrous sulphate, were evaluated for their effectiveness in improving dye fixation. The results indicated that tannic acid combined with ferrous sulphate provided superior colour strength on textile fabrics. The objective colour evaluation showed stronger colour intensity with this combination. The study also assessed the durability of algae-pigment-dyed textiles through tests for washing fastness, rubbing fastness, perspiration resistance, and dry cleaning. While the results were promising, improvements are still needed to match the performance of commercial dyes. Pollution analysis of the final effluent from the dyeing process revealed that all key parameters (BOD, COD, pH, colour, TDS, and TSS) were within acceptable standards. Phycocyanin pigments offer a sustainable alternative for textile colouration, though future research should focus on optimizing the economic feasibility of the dye extraction process.