The apparel industry faces strong global competition and firms must balance product quality with production efficiency. Defects such as misaligned seams, skipped stitches, and broken threads drive up waste, rework, and costs while weakening competitiveness. Researchers have used Six Sigma and Total Quality Management (TQM) to address these issues, and their studies show improvements in quality, cost, and productivity. Yet no study, to the best of our knowledge, has combined Six Sigma and TQM in a single framework that both reduces garment defects and improves sigma performance. This study applies the DMAIC cycle with TQM tools including Pareto charts, Cause–effect diagrams, and Standard Operating Procedures (SOP) to reduce sewing defects at Best Shirt Limited. The framework reduced defect rates and raised the sigma level from 2.1592 to 2.5427. These results confirm that integrating Six Sigma and TQM provides a practical path to sustainable quality improvement in garment manufacturing.