Impulsivity and emotion impairments have been noted in individuals with gambling disorder (GD). However, little research has investigated the influence of impulsivity and emotions on the severity of gambling in clinical populations. This study aimed to examine: (i) differences in emotions and impulsivity traits according to the severity of gambling in individuals with GD, (ii) the mediating effects of emotion in the relationship between impulsivity traits and gambling severity, and (iii) the predictive effects of emotion and impulsivity traits on GD severity. The study included 214 participants seeking treatment for GD who completed assessments for emotions (Patient Health Questionnaire-9 [PHQ-9], 7-item Generalized Anxiety [GAD-7]), impulsivity traits (Barratt Impulsiveness Scale [BIS], Self-control Scale [SCS]), and GD severity (DSM-5). Participants were categorized into mild (n = 78), moderate (n = 63), and severe (n = 73) gambling severity groups. Significant differences in emotions and impulsivity traits were observed across these groups. The severe GD group exhibited higher levels of depression, anxiety, and impulsivity traits, along with lower self-control, compared to the moderate and mild groups. Mediation analyses demonstrated that negative emotions mediated the association between impulsivity traits and the severity of gambling. More specifically, the indirect effects of impulsivity traits through PHQ-9 and GAD-7 were found to be significant, indicating a mediating role of emotions. Moreover, a predictive model incorporating emotion and impulsivity traits showed moderate accuracy in predicting the severity of gambling, with an area under the receiver operating characteristic curve of 0.714. This study highlights the distinct pathways through which impulsivity traits operate and emphasizes the need for prevention and treatment strategies that consider impulsivity traits and emotions for different levels of gambling severity.