The Turkish community living in Europe has an increased risk for suicidal ideation and attempted suicide. Online self-help may be an effective way of engagement with this community. This study will evaluate the effectiveness of a culturally adapted, guided, cognitive behavioural therapy-based online self-help intervention targeting suicidal ideation for Turkish adults living in the Netherlands and in the UK.This study will be performed in two phases. First, the Dutch online intervention will be adapted to Turkish culture. The second phase will be a randomized controlled trial with two conditions: experimental and waiting-list control. Ethical approval has been granted for the trials in London and Amsterdam. The experimental group will obtain direct access to the intervention, which will take 6 weeks to complete. Participants in the waiting-list condition will obtain access to the modules after 6 weeks. Participants in both conditions will be assessed at baseline, post-test and 3 months post-test follow-up. The primary outcome measure is reduction in frequency and intensity of suicidal thoughts. Secondary outcome measures are self-harm, attempted suicide, suicide ideation attributes, depression, hopelessness, anxiety, quality of life, worrying and satisfaction with the treatment.