In a dynamic business environment, human resource (HR) flexibility has emerged as a key factor in improving organizational performance and in potentially influencing employee outcomes. However, research on the complex cross-level effects of HR flexibility on employee outcomes remains underexplored. This study addresses this research gap by focusing on HR flexibility and its impact on employee creativity. Drawing on social information processing (SIP) theory, we present a novel model that elucidates the mechanisms through which HR flexibility promotes employee creativity and identifies the boundary conditions under which this effect is most pronounced. Specifically, we argue that perceived HR strength and career satisfaction play serial mediating roles in the relationship between HR flexibility and employee creativity, and that employer brand positively moderates this relationship. Our arguments are supported by a sample of 344 employees and 72 senior HR managers from financial services companies in China. Our work applies SIP theory to deepen the understanding of HR flexibility and contributes to the literature on HR flexibility and creativity.