The purpose of this study was to verify whether tobacco use influenced treatment outcome in a population of treatment seeking individuals with gambling disorder. Gambling disorder is defined as persistent and maladaptive gambling behaviour which meets four or more outlined criteria in the DSM-5. Tobacco use is the most frequent comorbidity with gambling disorder. A total of 676 treatment seeking individuals with gambling disorder were assessed at the National Problem Gambling Clinic in London. We analysed differences in socio-demographic, clinical and gambling variables between smokers and non-smokers and the relation between smoking behaviour and treatment completion and outcome. 46.4% (314) of our sample were daily tobacco users and were significantly younger, less likely to be in a stable relationship, more likely to be unemployed and have a lower education level. They were also significantly more likely to score higher on the AUDIT-C score and were significantly more likely to have used drugs in the last 30 days. There was no significant difference in PGSI score between smokers and non-smokers. We found that tobacco smokers did not have higher PGSI scores than non-smokers. Moreover, there was no significant difference between tobacco users and nonusers in terms of treatment completion and treatment outcome.