Background: In many nations, suicidality in young people has increased with a range of factors suggested to explain this, including increased attention on problem gambling as a risk factor for suicidality. Few studies have examined this specifically for young adults or since gambling has become more widely available, online, and normalised. Methods: A cross-sectional online survey collected data from 3549 16-24-year-olds living in Britain. Associations between problem gambling and past year suicidal thoughts and suicide attempts were examined in a series of regression models, with and without adjustment for sociodemographic factors, alcohol use, social media and gaming behaviour, anxiety, loneliness and impulsivity. Results: 37·0% (95%CI: 25.7-48.3) of young men who had attempted suicide in the past year were problem gamblers, compared with 3.6% (2.5-4.5) of young men who had not. Equivalent estimates for young women were 14·4% (6.4-22.4) and 2.0% (1.3-2.7). The unadjusted odds of attempted suicide were 15·1 (8.2-27.9) times higher among male problem gamblers and 8·0 (4.0-16.0) times higher among female problems gamblers. For both men and women, the relationship attenuated but remained significant taking other factors into account. Interpretation: Problem gambling appears to be a risk factor for suicide attempts in young people. This relationship persists once anxiety, impulsivity and life satisfaction are taken into account suggesting other mechanisms, like the harms experienced by those who gamble problematically, or gamble to cope with life stressors, underpin this relationship. Young people with gambling problems should be viewed as high-risk for suicidality. Funding: Funded by Wellcome Trust (no: 200306/Z/15/Z). Declaration of Interests: HW is the Deputy Chair of the Advisory Board for Safer Gambling, which provides advice to the Gambling Commission on policy and regulatory issues. In the last three years, she has worked on one project funded by GambleAware along with SM. HW runs a research consultancy, providing research services to public and third sector bodies. She does not and has not provided consultancy services for the gambling industry. SM declares no further competing interests. Ethics Approval Statement: Ethical approval for the study was granted by London School of Hygiene and Tropical Medicine’s Ethics Review Panel (ref: 15960).