Background Surgical services were poorly prepared for the COVID-19 pandemic, leading to widescale disruption to elective activity. This study aimed to identify actionable priorities to strengthen pandemic preparedness of surgical and hospital systems. Methods This study pooled data from three international, prospective cohort studies including patients who had a positive SARS-CoV-2 test result in the seven days before or within 30 days after surgery. Patients were included across four pandemic time periods: Period 1 (January–May 2020), Period 2 (June–July 2020), Period 3 (October 2020), and Period 4 (December–March 2022). The primary outcome measure was 30-day postoperative mortality. Hierarchical logistic regression models were developed to explore association between pandemic periods (primary analysis) and hospital-level preparedness (secondary analysis) on 30-day postoperative mortality. Hospital preparedness was classified in to poorly-, moderately-, and highly-prepared tertiles based on Surgical Preparedness Index (SPI) score. Findings A total of 31,751 patients were included from 1589 hospitals and 102 countries. From Period 1 through to Period 4 there was a decrease in the proportion of patients aged ≥70 years and with ASA grades 3–5.30-day postoperative mortality fell from Period 1 (18.4% [1378/7502]), Period 2 (9.9% [219/2234], adjusted odds ratio (aOR) 0.65, 95% confidence interval (CI) 0.53–0.78), Period 3 (10.5% [246/2427], aOR 0.60, 95% CI 0.50–0.71), through to Period 4 (5.8% [1132/19,588], aOR 0.33, 95% CI 0.30–0.37). During Period 4, SARS-CoV-2 vaccinated patients had lower mortality compared to unvaccinated patients (4.9% [603/12,361] versus 7.4% [529/7178], aOR 0.49, 95% CI 0.42–0.57). Compared to poorly-prepared hospitals (11.2% [1019/9071]), moderately-prepared (9.4% [857/9071], aOR 0.84, 95% CI 0.75–0.94) and highly-prepared hospitals (5.8% [530/9071], aOR 0.70, 95% CI 0.62–0.80) had lower mortality. Interpretation Postoperative mortality decreased over the course of the COVID-19 pandemic and was lower in better prepared hospitals. Hospitals are critical national infrastructure and strengthening their preparedness by developing formal pandemic plans, establishing patient and procedure prioritisation protocols, and ring-fencing surgical beds would ensure safer surgical care during future pandemics. Funding National Institute for Health and Care Research, United Kingdom.