BACKGROUND: Suicide prevention gatekeeper Training (GKT) is a frequently used suicide prevention intervention, however, there is still limited information about its long-term impact and effectiveness of online delivery. AIMS: The current study aimed to test the effectiveness of online GKT compared to in-person GKT in improving participant training outcomes. METHODS: A non-randomised comparison of pre-, post- and six-month follow-up data was conducted. In total 545 people participated in GKT, 317 in SafeTALK in-person sessions and 228 in online "Start" GKT by LivingWorks. Main outcome measures included: perceived knowledge; perceived preparedness; gatekeeper efficacy; and gatekeeper reluctance to intervene. RESULTS: Linear mixed model analysis demonstrated a significant effect for time for both modes of delivery for all four outcome measures. Post-hoc testing revealed that significant improvement in all outcomes were maintained above baseline at six-months following online and in-person training. CONCLUSIONS: Online training performed as good, or better than in-person GKT, on measured outcomes demonstrating utility and effectiveness of the modality for use in suicide prevention training practices. Findings additionally indicate that online training may reach participants that in-person programs do not. This study provides evidence that Online GKT has significant utility in addressing a crucial need for online alternatives to evidence-based suicide prevention training.