Although research has examined disparities in suicidal ideation across multiple groups, few investigations have analyzed such disparities in the context of COVID-19 pandemic. Furthermore, there is limited research on differences within and across countries, further limiting the extent to which meaningful comparisons can be made. Therefore, this study examines risk and protective factors of suicidal ideation during COVID-19 lockdown in adults across five countries. Adults (N = 2,509) from the United States, Italy, Spain, Saudi Arabia, and India completed a survey to measure suicidal ideation, recent drug use, and sociodemographic factors. Prevalence of suicidal ideation was assessed using simple and multivariable logistic regression models, and severity of suicidal ideation was analyzed via a multinomial multivariable logistic regression. Cohen's d statistics were reported for all analyses to report effect size. In the United States subsample, racial/ethnic minorities endorsed a significantly greater prevalence of suicidal ideation compared to their White peers (aOR = 2.31, 95% CI: 1.26–4.27, d = 0.46). However, no significant racial differences in suicidal ideation were found in other countries. Past 90-day illicit drug use was associated with greater prevalence (aOR = 1.38, 95% CI: 1.06–1.80, d = 0.18) and severity (aRRR = 2.17, 95% CI: 1.33–3.53, (aRRR = 0.43) of suicidal ideation during COVID-19 lockdown. This study further highlights the social disparities that exist in suicidal ideation during COVID-19 lockdown in international samples, for which greater medical and mental health interventions are critical. As such, targeted multicomponent interventions that address substance use are important for reducing the rising prevalence and severity of COVID-related suicidal ideation.