Self-control has been related to positive student outcomes including academic performance of college students. Because of the critical nature of the first semester academic performance for engineering students in terms of retention and persistence in pursuing an engineering degree, this study investigated the relationship between freshmen engineering students' scores on the Brief Self-Control Scale and first semester GPA. To identify the unique explanatory contribution of self-control beyond incoming academic performance differences, the effect of ACT Composite scores was statistically removed from the sample of three cohorts of freshmen engineering students (n = 1295 total). The results showed the measure of self-control explained on average 4.2% of the residual variability in first semester GPA, after accounting for the variability explained by ACT scores. Based on results of this study, self-control predicted between 27%-42% as much of the variance in first semester GPA as did ACT scores, a much-used high stakes measure frequently used for decisions such as program admittance or mathematics course placement. Thus self-control is a nontrivial predictor of academic performance. Based on post hoc analysis, relevant self-control behaviors might manifest themselves in time and study management since there was a significant correlation between self-control scores and scores on the MSLQ time and study management measure. These results have implications for both how much of an impact positive self-control may have on freshmen engineering academic performance, while also offering potential avenues to support students in bolstering aspects of this personality trait through a focus on strengthening time and study management skills.