Aims: Lithium has long been believed to reduce the risk of suicide and suicidal behaviour in people with mood disorders. Previous meta-analyses appeared to support this belief, but excluded relevant data due to the difficulty of conducting meta-analysis of rare events. The current study is an updated systematic review and meta-analysis that includes all eligible data, and evaluates suicide, non-fatal suicidal behaviour (including suicidal ideation) and suicide attempts. Methods: We searched PubMed, PsycINFO and Embase and some trial registers. We included all randomised trials comparing lithium and placebo or treatment as usual in mood disorders published after 2000, to ensure suicide was reliably reported. Trial quality was assessed using the Cochrane Risk of Bias tool. Pooled data were analysed using Fisher's Exact test. In addition, meta-analysis was conducted using various methods, prioritizing the Exact method. All trials were included in the analysis of suicide initially, regardless of whether they reported on suicide or not. We conducted a sensitivity analysis with trials that specifically reported on suicides and one that included trials published before 2000. Pre-specified subgroup analyses were performed involving suicide prevention trials, trials excluding people already taking lithium, trials involving people with bipolar disorder exclusively and those involving people with mixed affective diagnoses. Non-fatal suicidal behaviour and suicide attempts were analysed using the same methods, but only trials that reported these outcomes were included. PROSPERO registration: CRD42021265809. Results: Twelve eligible studies involving 2578 participants were included. The pooled suicide rate was 0.2% for people randomised to lithium and 0.4% with placebo or treatment as usual, which was not a statistically significant difference; odds ratio (OR) = 0.41 (95% confidence interval 0.03–2.49), p = 0.45. Meta-analysis using the Exact method produced an OR of 0.42 (95% confidence interval 0.01–4.5). The result was not substantially different when restricted to 11 trials that explicitly reported suicides and remained statistically non-significant when including 15 trials published before 2000 (mostly in the 1970s). There were no significant differences in any subgroup analysis. There was no difference in rates of all non-fatal suicidal behaviour in seven trials that reported this outcome, or in five trials that reported suicide attempts specifically. Meta-analyses using other methods also revealed no statistically significant differences. Conclusions: Evidence from randomised trials is inconclusive and does not support the idea that lithium prevents suicide or suicidal behaviour.