<p>Gambling is a public health problem that affects many people in many ways. One of the most serious effects is on people's mental health and suicidal ideation. This study has two main aims: 1) To analyse the differences between the clinical population (i.e., individuals with gambling disorder) and the general population in terms of gambling severity, suicidal ideation, and mental health; and 2) to test the mediating role of mental health in the relationship between gambling severity and suicidal ideation in people with gambling disorder and the general population. A total of 318 participants were included in the study: 153 gamblers undergoing treatment for gambling disorder (<i>M</i>_age = 44.38, <i>SD</i> = 12.48, 81% males) and 165 individuals from the general population (<i>M</i>_age = 47.57, <i>SD</i> = 13.52, 26.67% males). Two structural equation models were conducted to test the mediating role of mental health issues (i.e., depression, anxiety, hostility, somatisation, and obsessive–compulsive) in the relationship between gambling severity and suicidal ideation. The results show no significant differences in mental health between the population with gambling disorder and the general population. However, the relationship between gambling severity and suicidal ideation appears to be mediated by mental health, both in the clinical and general populations. Findings show the importance of addressing mental health to prevent suicidal ideation. Given the high prevalence of suicidal ideation in individuals with gambling disorder, the assessment and treatment of gambling problems and mental health is strongly recommended. Results also highlight the importance of transdiagnostic protocols that address mental health, with a particular focus on suicidal ideation.</p>