Background: Both fatal and nonfatal suicidal behaviours are important complications of mental, neurological, and substance use disorders (MNSDs) worldwide. We aimed at quantifying the association of suicidal behaviour with MNSDs in Low and Middle Income Countries (LMICs) where varying environmental and socio-cultural factors may impact outcome. Methods: We conducted a systematic review and meta-analysis to report the associations between MNSDs and suicidality in LMICs and the study-level factors of these associations. We searched the following electronic databases: PUBMED, PsycINFO, MEDLINE, CINAHL, World Cat, and Cochrane library for studies on suicide risk in MNSDs, with a comparison/control group of persons without MNSDs, published from January 1, 1995 to September 3, 2020. Median estimates were calculated for relative risks for suicide behaviour and MNSDs, and when appropriate, these were pooled using random effects metanalytic model. This study was registered with PROSPERO, CRD42020178772. Results: The search identified 73 eligible studies: 28 were used for quantitative synthesis of estimates and 45 for description of risk factors. Studies included came from low and upper middle-income countries with a majority of these from Asia and South America and none from a low-income country. The sample size was 13,759 for MNSD cases and 11,792 hospital or community controls without MNSD. The most common MNSD exposure for suicidal behaviour was depressive disorders (47 studies (64%)), followed by schizophrenia spectrum, and other psychotic disorders (28 studies (38%)). Pooled estimates from the meta-analysis were statistically significant for suicidal behaviour with any MNSDs (odds ratios (OR) = 1∙98 (95%CI = 1∙80–2∙16))) and depressive disorder (OR = 3∙26 (95%CI = 2∙88–3∙63))), with both remaining significant after inclusion of high-quality studies only. Meta-regression identified only hospital-based studies (ratio of OR = 2∙85, CI:1∙24–6∙55) and sample size (OR = 1∙00, CI:0∙99–1∙00) as possible sources of variability in estimates. Risk for suicidal behaviour in MNSDs was increased by demographic factors (e.g., male sex, and unemployment), family history, psychosocial context and physical illness. Interpretation: There is an association between suicidal behaviour and MNSDs in LMICs, the association is greater for depressive disorder in LMICs than what has been reported in High Income Countries (HICs). There is urgent need to improve access for MNSDs care in LMICs. Funding: None.