Previous research has shown that depression is an important predictor for suicidal ideation and that depression, addictive behaviors, and suicidal ideations are highly associated with each other. However, no studies have specifically investigated the role of addictive behaviors (i.e., alcohol use, gambling) as moderators on the association between depression and suicidal ideation among Korean college students. This study examined (1) the association between depression and suicidal ideation using Depression, Anxiety and Stress Scale (DASS-21) and five selected items from the Youth Risk Behavior Surveillance System (YRBSS), and (2) the moderating roles of alcohol use and problem gambling using Alcohol Use Disorder Identification Test (AUDIT) and Problem Gambling Severity Index (PGSI). We collected data from full-time students (n = 870) enrolled at 14 universities throughout South Korea using a self-reported paper-pencil survey conducted on college campuses. More than half of the total sample (52.3%, n = 450) reported either alcohol use or gambling, and findings revealed that depression, alcohol use, and gambling are associated with suicidal ideation. We found a significant moderating effect of alcohol use on the relationship between depression and suicidal ideation (ß = .151, p < .001); whereas, gambling had no significant moderating effect on the relationship (ß = .054, p < .276). The influence of depression on suicidal ideation was greater for Korean college students who used high levels of alcohol compared to those who used low levels of alcohol. The results suggest that alcohol use is an important modifiable factor for suicidal ideation especially in students with depression, and provide a foundation for future research aimed at understanding complex and nuanced mechanisms linking depression, addictive behaviors, and suicidal ideation.