Social distancing measures adopted in various countries to mitigate the impact of the COVID-19 pandemic can lead to unwanted effects on their populations' health and behaviors. This study aimed to investigate smoking behavior in the Brazilian adult population during the COVID-19 pandemic and analyze factors associated with the increase in cigarette consumption. An online survey was performed, and the final sample included 45,160 individuals. The study used post-stratification weights and calculated crude prevalence ratios (PR) and adjusted by sex, age, and schooling, and respective 95% confidence intervals (95%CI). Poisson regression models with robust variance were applied to analyze associations between increased cigarette consumption and sociodemographic variables and adherence to social distancing, quality of sleep, state of mind, and changes in work and earnings. Prevalence of smokers was 12% (95%CI: 11.1-12.9), 34% of whom reported an increase in cigarette consumption. The increase was greater among women (PR = 1.27; 95%CI: 1.01-1.59) and individuals with incomplete secondary schooling (PR = 1.35; 95%CI: 1.02-1.79). The increase in cigarette consumption was associated with worse quality of sleep, feeling isolated from family members or sad, depressed, or anxious, loss of earnings, and worse self-rated health. Health promotion strategies, smoking prevention, and encouragement for smoking cessation, as well as mental health interventions, should be continued and reinforced in the context of social distancing during the COVID-19 pandemic.