<p>With a growing population of employees moving from traditional to home offices and loneliness becoming a global concern, we seek to examine daily predictors of workplace loneliness among full-time remote workers. In this study, we propose that sleep as a source of vigor provides employees with sufficient resources to engage in workplace interactions with coworkers, which helps reduce their feeling of workplace loneliness. We tested our prediction about the indirect effect of sleep quality on loneliness using a sample of 107 employees working fully remotely prior to the COVID-19 pandemic and a sample of 135 employees working remotely full time during the first wave of the COVID-19 pandemic. In both samples, we surveyed employees for 5 consecutive workdays, measuring their sleep quality at night, vigor in the morning, the amount of interaction with coworkers during the workday, and workplace loneliness during the day. The results indicated that for employees who were sent to work fully remotely due to the pandemic, but not for employees who chose to work remotely prior to the pandemic, higher-quality sleep was related to reduced workplace loneliness indirectly, via increased morning vigor and interactions with coworkers during the day.</p>