Obesity is considered as one of the entrance point of multimorbidity and has an impact on physical and mental health. While some evidence points out to a possible relationship between obesity, multimorbidity and suicidal spectrum, little provide a direct association. Thus, the aim of the present study was to examine the co-occurring effect of both multimorbidity and obesity on suicidal ideation. Methods A cross-sectional analysis of the Canadian Community Health Survey data was conducted. A weighted sample of young adults (18 to 30 years-old) with obesity, from the province of Quebec, of the 2005 (n=394) and 2015–2016 (n=295) cycles were investigated independently. Multimorbidity, suicidal ideation, and health behaviours were self-reported. Results The prevalence of physical multimorbidity was 15% in 2005 and 18% in 2015–2016. Adjusted logistic regressions showed an association between multimorbidity and suicidal ideation (2005: OR 3.59, 95% CI 1.89-6.81; 2015–2016: OR 3.72, 95% CI 1.88-7.36). Among covariates, the significant association of sex (OR 1.98; 95% CI 1.16-3.37) and educational status (OR 3.27; 95% CI 1.49-7.18) in the 2005 cycle, were not replicated in the 2015–2016 cycle (education: OR 0.93; 95% CI 0.46-1.87; sex (OR 0.90; 95% CI 0.48-1.69). Finally, our results suggest no consistent association between health behaviours and suicidal ideation.Conclusion Multimorbidity seems to be associated with suicidal ideation among those with obesity. Attention should be given to multimorbidity management within obesity-related interventions for young people, as the development of suicidal ideation may also be prevented.