PurposeExploiting a unique measure of hostile takeover exposure principally based on the staggered adoption of state legislations, the authors investigate how external audit quality is influenced by the discipline of the takeover market. External auditors and the takeover market both function as important instruments of external corporate governance.Design/methodology/approachThe authors execute a standard regression analysis and run a variety of robustness checks to minimize endogeneity, namely, propensity score matching (PSM), entropy balancing, an instrumental-variable analysis, Generalized method of moment (GMM) dynamic panel data analysis and Lewbel's (2012) heteroscedastic identification.FindingsThe authors’ immense sample spans half a century, encompassing nearly 180,000 observations and 17 takeover-related state legislations, one of the largest samples in the literature in this area. The authors’ results suggest that firms with more takeover exposure are significantly less likely to use Big N auditors. Therefore, a more active takeover market results in poorer external audit quality, corroborating the substitution hypothesis. The discipline of the takeover market substitutes for the necessity for a high-quality external auditor. Specifically, a rise in takeover susceptibility by one standard deviation lowers the probability of using a Big N auditor by 4.29%.Originality/valueThe authors’ study is the first to examine the effect of the takeover over market on audit quality using a novel measure of hostile takeover susceptibility mainly based on the staggered implementation of state legislation. Because the enactment of state legislation is beyond the control of any firm individually, it is plausibly exogenous. The authors’ results therefore probably reflect a causal influence rather than merely a correlation.