Widespread use of social media across work and non-work boundaries has heightened concerns about employee engagement in the contemporary workforce. This study examines how employees’ boundary management preferences influence their work communication on social media, and how these factors impact their engagement. Results from three waves of survey data (N = 361) demonstrate that work communication mediates the relationship between employee boundary preferences and engagement, supporting the hypothesized causal structure over alternative models. Overall, the findings contribute a novel perspective on employee engagement by showing that mediated work communication plays a central role in constructing engagement, rather than merely demonstrating it. We discuss how organizations can leverage this knowledge to address critical concerns about workplace (dis)engagement in the digital age.