Background: Historically, differences in timely reperfusion and outcomes have been described in females who suffer ST-segment elevation myocardial infarction (STEMI). However, there have been improvements in the treatment of STEMI patients with contemporary Percutaneous Coronary Intervention (PCI) strategies. Methods: Comparisons between sexes were performed on STEMI patients treated with primary PCI over a 4-year period (January 1, 2017–December 31, 2020) from the Queensland Cardiac Outcomes Registry. Primary outcomes were 30-day and 1-year cardiovascular mortality. Secondary outcomes were STEMI performance measures. The total and direct effects of gender on mortality outcomes were estimated using logistic and multinomial logistic regression models. Results: Overall, 2747 (76% male) were included. Females were on average older (65.9 vs. 61.9 years; p < 0.001), had longer total ischemic time (69 min vs. 52 min; p < 0.001) and less achievement of STEMI performance targets (<90 min) (50% vs. 58%; p < 0.001). There was no evidence for a total (odds ratio [OR] 1.3 (95% confidence interval [CI]: 0.8–2.2; p = 0.35) or direct (adjusted OR 1.2 (95% CI: 0.7–2.1; p = 0.58) effect of female sex on 30-day mortality. One-year mortality was higher in females (6.9% vs. 4.4%; p = 0.014) with total effect estimates consistent with increased risk of cardiovascular mortality (Incidence rate ratio [IRR]: 1.5; 95% CI: 1.0–2.3; p = 0.059) and noncardiovascular mortality (IRR: 2.1; 95% CI: 0.9–4.7; p = 0.077) in females. However, direct (adjusted) effect estimates of cardiovascular mortality (IRR: 1.0; 95% CI: 0.6–1.6; p = 0.94) indicated sex differences were explained by confounders and mediators. Conclusion: Small sex differences in STEMI performance measures still exist; however, with contemporary primary PCI strategies, sex is not associated with cardiovascular mortality at 30 days or 1 year.