Background: COVID-19 disrupted lives globally, and to combat it, various countries including India imposed lockdown and other restrictions. This study was conducted to estimate the prevalence of poor sleep quality among Indian adults in 18–30-year age-group and factors associated with it during lockdown. Methods: This was an online survey-based cross-sectional study conducted in May 2020 after 6 weeks of lockdown in India. Information regarding sociodemographic profile, screen time, physical activity, substance use, caffeine intake, and sleep habits during lockdown was collected. Pittsburgh sleep quality index was used to assess the sleep quality. Descriptive analysis was performed. Results: A total of 244 study participants were included in the study, out of which 59% (144) were males and mean age was 24.1 years. Physical activity was decreased among 138 (56.6%) and screen time of more than 4 hours among 152 (62.3%) study participants. Poor sleep quality was reported by 47.1% (115) and sleep duration was decreased among 24.6% (60) study participants. Younger age, living in a containment zone, optimal use of available time, and decreased sleep duration were found to be associated with poor sleep quality. Conclusion: Lockdown affected sleep quality of the study participants adversely, delaying sleeping and waking times. It is important to ensure minimum disruption of day-to-day schedule of people even during such restrictions. Living in a containment zone was found to be significantly associated with poor sleep quality. Authorities should see to it that people living in such zones should be given priority and counseled appropriately.