Background Sepsis is a leading cause of mortality and morbidity worldwide. South African adult public critical care units experience incidences of sepsis on an ongoing basis. Nurses caring for mechanically ventilated adult patients in intensive care units (ICUs) need to base their nursing care on “surviving sepsis campaign” (SSC) guidelines to properly manage sepsis. Adequate knowledge on sepsis guidelines remains crucially indicated for nurses as they endeavor to maintain asepsis in critically ill patients. Purpose This study was conducted to assess the effect of an educational intervention on nurses' knowledge and practices of sepsis in mechanically ventilated adult patients in public ICUs. Methods An intervention study, with quasi-intervention two-group, pretest–posttest design, was used to collect data using a self-administered, structured, pretest and posttest questionnaire designed to measure nurses' knowledge and practices on sepsis related to mechanical ventilation. The study was conducted between June and October 2018. An educational intervention was developed and validated. Five purposively selected public ICUs in the Eastern Cape, South Africa, were selected and assigned to three groups: Intervention Group 1 (ICUs 1 and 2), which received the full intervention (containing a 20-minute PowerPoint presentation, printed materials based on sections of the SSC guidelines, and monitoring visits bimonthly for 3 months); Intervention Group 2 (ICUs 3 and 4; receiving the same as Intervention Group 1 but with no monitoring visits); and the control group (ICU 5; receiving no intervention). Results One hundred seventeen nurses completed the questionnaires at pretest, and 94 completed the questionnaires at posttest, producing a response rate of 79% and 80%, respectively. The results revealed a significant knowledge score increase between pretest and posttest for both Intervention Group 2 (53.28 ± 14.39 and 62.18 ± 13.60, respectively; p = .004) and the control group (56.72 ± 13.72 and 70.05 ± 12.40, respectively; p = .001). Similarly, a recommended practice score increase was shown for Intervention Group 2 (58.8 ± 9.63 and 62.80 ± 9.52, respectively), and a significant increase was shown for the control group (56.72 ± 7.54 and 63.29 ± 5.89, respectively; p = .002). Intervention Group 1 showed a detectable but not significant decline in knowledge (57.72 ± 13.99 and 54.61 ± 12.15, respectively) and recommended practice (61.22 ± 8.66 and 60.33 ± 7.83, respectively) scores. Conclusions The availability of SSC guidelines was found to have increased knowledge on sepsis related to mechanical ventilation, although including monitoring visits as part of the educational intervention was not found to have a positive effect on increasing knowledge and practices. Further studies are required to explore factors contributing to improving knowledge and practices on sepsis related to mechanical ventilation and the effect that various educational interventions have in this context.