Corporate social responsibility (CSR) is increasingly adopted as a strategic tool to enhance firms’ sustainability and financial performance (CFP). However, despite extensive research, evidence on the underlying factors influencing CSR and CFP remains scarce. This study addresses this gap by exploring the role of employee engagement as one possible mechanism through which CSR initiatives may translate into CFP. Adopting a systematic literature review on papers published in 2019–2024 and a comparative case study methodology, the paper analyzes two Italian firms characterized by different configurations of CSR practices, including varying degrees of formalization and integration into organizational culture. The study leverages semi-structured interviews with management, employee surveys capturing perceptions of CSR and engagement, and firm-level financial indicators. The findings suggest that CSR contributes to CFP through some dimensions of higher engagement and only when CSR is perceived by employees as authentic and embedded in everyday organizational practices. The paper contributes to the literature on the factors influencing the relationship between firms’ CSR activities and CFP and the role played by employee engagement. Moreover, it offers implications for managers to design CSR strategies that create both sustainable and financial value.