Experiencing poor, unrefreshing sleep is a common occurrence for individuals with chronic pain. Sleep disturbance predicts not only greater pain and disability, but also heightened negative affect and reduced positive affect in individuals with chronic pain. Such fluctuations in affect have been linked with more negative and fewer positive social events. For those with chronic pain, negative social relations can exacerbate pain, whereas positive social interactions can help decrease disability. Thus, exploring the sleep‒social functioning process in chronic pain may be one way to improve daily functioning and quality of life. The current study examined positive and negative affect as two parallel mediators of the within-day relations between sleep quality and positive and negative social events in individuals with chronic pain. For 21 days, electronic daily diary reports were collected from 220 individuals with fibromyalgia, a condition characterized by widespread chronic pain. Within-person relations among reports of last night’s sleep quality, afternoon affects and pain, and evening social events were estimated via multilevel structural equation modeling. Findings showed that positive affect mediated both the sleep quality‒positive social events and sleep quality‒negative social events relations. That is, greater than usual sleep disturbance last night predicted afternoon reports of lower than usual positive affect. Low positive affect, in turn, predicted evening reports of fewer than usual positive social events and more than usual negative social events that day, controlling for the effects of afternoon pain. In addition, negative affect mediated the sleep quality‒negative social events link. That is, greater than usual sleep disturbance last night predicted afternoon reports of higher than usual negative affect, which, in turn, predicted evening reports of more than usual negative social events that day, controlling for the effects of afternoon pain. Of the three significant mediated paths, the sleep quality‒positive affect‒positive social events path was the strongest in magnitude. Thus, a night of poor sleep can have an impact on social events the next day in those with chronic pain by dysregulating affect. Further, findings highlight the key role of positive affect in the sleep‒social functioning process and potential socio-affective benefits of sleep interventions in chronic pain.