Background: It is important medical students, as tomorrow’s doctors, have knowledge of physical activity (PA) guidelines. Previous data suggests only 14.9% of medical students knew adult PA guidelines. This study aimed to assess how a novel flipped classroom intervention impacted undergraduate medical students’ knowledge of PA guidelines and their confidence applying these in clinical practice. Methods and Results: This study utilised a prospective repeat measures quantitative design to evaluate the educational intervention. Survey results of the intervention group were compared to the comparison group. 45% of students who received the intervention knew adult guidelines, compared to 12% of students who did not receive the intervention (χ²(2, N = 244) = 33.07, p < 0.001). 39% of the intervention group knew child guidelines, compared to 20% who did not receive the intervention (χ²(2, N = 244) = 10.59, p = 0.001). The intervention group felt more confident in PA training and asked for less PA training in the future. Conclusion: The results suggest a flipped classroom intervention had a positive impact on medical students’ knowledge of PA guidelines, and confidence in PA training. Further research is required to assess longer-term impacts of this teaching and follow-up the same year group pre- and post-intervention.