Grounded in Morgan and Hunt’s Commitment-Trust Theory of Relationship Marketing, the current research examines the effects of dialogic communication (DC) of CSR through digital media on brand loyalty (LOYT) mediated by customers’ online brand community engagement (OBCE) and brand trust (TRUST). To test the proposed mediation model, we conducted a national survey with a representative sample (N = 1022), randomly drawn from Qualtrics’ U.S. panel. After ensuring the validity, reliability and model fit of the measurement model, we tested the postulated model using a structural equation modeling procedure. All proposed hypotheses were supported showing (1) the direct effects of dialogic communication on CSR authenticity and OBCE; (2) the direct effects of OBCE on brand trust and brand loyalty; (3) indirect effects of dialogic communication on brand loyalty through OBCE and brand trust; and (4) the indirect effects of CSR authenticity on brand loyalty through OBCE and brand trust. In accordance with the theory of customer brand engagement, this study found that OBCE had the largest effect on brand loyalty. A notable contribution of the current research is that OBCE was driven by customers’ perceptions of a firm’s dialogic communication in CSR communication through digital media, which was partially mediated by perceived CSR authenticity. The results provide brand managers with practical implications—that is, a brand can build an online brand community and foster customer engagement when its communication is dialogic rather than monologic or purely promotional. Another noteworthy finding is that both dialogic communication and CSR authenticity has no significant direct effect on loyalty. The effect from DC to LOYT was fully mediated via OBCE. The effect of CSR authenticity on LOYT was fully mediated through OBCE and TRUST. The results of mediation analysis indicate that the specific mediation through TRUST was larger than the specific mediation through OBCE, although both were significant. Another notable finding is the effect of OBCE on loyalty. The results of mediation analysis show that the direct effect is stronger than the indirect effect via trust. The results give practitioners significant implications and justification to nurture an online brand community through communicating the company’s CSR activities.