BACKGROUND: Suicidal ideation may lead to deliberate self-harm which increases the risk of death by suicide. Globally, the main cause of deliberate self-harm is depression. The aim of this study was to explore prevalence of, and risk factors for, suicidal ideation among men and women with common mental disorder (CMD) symptoms attending public clinics in Zimbabwe, and to determine whether problem solving therapy delivered by lay health workers can reduce common mental disorder symptoms among people with suicidal ideation, using secondary analysis of a randomised controlled trial. METHODS: At trial enrolment, the Shona Symptom Questionnaire (SSQ) was used to screen for CMD symptoms. In the intervention arm, participants received six problem-solving therapy sessions conducted by trained and supervised lay health workers, while those in the control arm received enhanced usual care. We used multivariate logistic regression to identify risk factors for suicidal ideation at enrolment, and cluster-level logistic regression to compare SSQ scores at endline (6 months follow-up) between trial arms, stratified by suicidal ideation at enrolment. RESULTS: There were 573 participants who screened positive for CMD symptoms and 75 (13.1%) reported suicidal ideation at baseline. At baseline, after adjusting for confounders, suicidal ideation was independently associated with being aged over 24, lack of household income (household income yes/no; adjusted odds ratio 0.52 (95% CI 0.29, 0.95); p = 0.03) and with having recently skipped a meal due to lack of food (adjusted odds ratio 3.06 (95% CI 1.81, 5.18); p < 0.001). Participants who reported suicidal ideation at enrolment experienced similar benefit to CMD symptoms from the Friendship Bench intervention (adjusted mean difference - 5.38, 95% CI -7.85, - 2.90; p < 0.001) compared to those who had common mental disorder symptoms but no suicidal ideation (adjusted mean difference - 4.86, 95% CI -5.68, - 4.04; p < 0.001). CONCLUSIONS: Problem-solving therapy delivered by trained and supervised lay health workers reduced common mental disorder symptoms among participants with suicidal thoughts who attended primary care facilities in Zimbabwe. TRIAL REGISTRATION: pactr.org ldentifier: PACTR201410000876178.