Individual differences in distress tolerance (DT), willingness to face internal discomfort, predict who is vulnerable to non-suicidal self-injury (NSSI). However, it is unclear to what extent within-person differences in DT predict periods of peak NSSI risk. We used short-term variation in DT as a model of acute NSSI risk among people with recurrent NSSI. We sampled momentary DT and NSSI outcomes four times per day across 14 consecutive days in a group of 119 adults who had significant histories of NSSI behavior. Momentary DT ratings had robust within-person correlations with concurrent NSSI thoughts and behaviors (rs = −0.43 and −0.20, respectively). Also, DT was a statistically significant, albeit weak, predictor of NSSI outcomes up to 3 h later, even when adjusting for continuity in NSSI. Negative urgency and experiential avoidance—DT’s conceptual neighbors—added predictive utility in within-person models of NSSI thoughts and behavior (e.g., collectively the 3 predictors accounted for more than a third of within-person variation in concurrent NSSI thoughts). We conclude that time-varying DT levels could be a meaningful model, and potentially intervention target, for NSSI in high-risk populations. Our study’s dataset, analysis code, and materials are available at https://osf.io/nz5q4/.