This research paper examines the transformation of sportswear from clothing designed exclusively for athletic performance into a dominant force in everyday global fashion. Drawing on secondary sources spanning academic journals, fashion history books, brand case studies, and archival records, the study traces this evolution from the 19th century to the present day. The findings reveal that the shift was driven by an interconnected set of forces: broader social and cultural changes, deliberate industrial and marketing strategies, technological innovation in fabric and garment engineering, high-profile designer collaborations, and the rise of fitness and lifestyle culture. The research concludes that sportswear is no longer a peripheral clothing category but a central expression of modern identity, reflecting the enduring relationship between culture, comfort, technology, and style.