The Coronavirus disease (COVID-19) pandemic has brought about drastic measures that have significantly altered the norms of daily living. These measures have affected human behaviors in disparate ways. This study seeks to understand the impact of the pandemic on physical activity and dietary behavior among adults living in Kuwait. A cross-sectional survey was conducted between 18 June and 15 July 2020, using a questionnaire disseminated through social media, including WhatsApp and Facebook. The target population was individuals aged 21 years or older living in the State of Kuwait. The study included 679 respondents; 57.9% were females, and 67.7% were Kuwaiti nationals. Both genders reported an increased consumption of vegetables, fruits, and carbohydrates, and a decreased consumption of fish and sugary drinks. Compared to males, females reported eating more during the outbreak than their pre-pandemic eating behaviors (32.3% vs. 35.9%, p < 0.05). Approximately one-third of respondents (33.1%) reported performing less than 30 min of physical activity or exercise in a week, and 36.4% of respondents rated their quality of sleep as 'poor' or 'very poor'. The rate of smoking cigarettes among males was significantly higher than in females (40.6% vs. 5.3%, p < 0.001). Physical activity was positively correlated with vegetable consumption and quality of sleep. Quality of sleep was negatively correlated with the consumption of sweets and snacks, just as the consumption of vegetables was negatively correlated with the consumption of sugary drinks. The overall negative impact of the COVID-19 pandemic in Kuwait necessitates the development of health promotion interventions to support positive physical activity and dietary behaviors using alternative coping strategies among the residents of Kuwait.