The digital economy has placed information technology (IT) at the core of value creation, especially in service firms that rely heavily on intangible resources, customer interaction, and agile processes. This paper explores the role of IT Resource-Based Theory (IT-RBT) in explaining how IT resources contribute to sustainable competitive advantage in service environments such as financial services, hospitality, healthcare, consulting, and digital platforms. While the classical Resource-Based View (RBV) emphasizes valuable, rare, inimitable, and non-substitutable resources, recent studies highlight the strategic importance of IT capabilities, data assets, digital platforms, and knowledge processes. This article proposes a comprehensive IT-RBT Competitive Advantage Framework tailored for service firms, integrating organizational IT capabilities, dynamic capabilities, data resources, and human capital. The findings show that IT-enabled services create superior performance outcomes by enhancing customer experience, operational efficiency, innovation, and agility.