The tendency for our minds to wander is a pervasive and disruptive influence on continued task performance. Models of sustained attention have implicated mind wandering, moments when attention has turned inwards toward task-unrelated thought, in characteristic patterns of worsening performance with greater time-on-task, known as the vigilance decrement. Despite their theoretical connection, associations between mind wandering and the vigilance decrement have not been investigated systematically. Across two studies (N = 730), we evaluated covariance between within-task change in rates of probe-caught mind wandering and patterns of worsening behavioral task performance that characterize the vigilance decrement. Bivariate growth curve models characterized patterns of intraindividual linear change in mind wandering alongside concomitant changes in task accuracy, response time (RT), and RT variability. Importantly, models assessing the covariance between intraindividual change in mind wandering and behavioral outcome measures confirmed that increases in mind wandering are associated with patterns of worsening behavioral performance with greater time-on-task. In addition, we investigated the role of several moderating factors associated with patterns of within-task change: self-reported task interest and motivation, and individuals' propensity for mind wandering, and mindfulness in their daily lives. These factors moderated either the overall level or rate of within-task change in mind wandering. Our results provide support for models of sustained attention that directly implicate mind wandering in worsening behavioral performance with greater time-on-task in continuous performance tasks requiring sustained attention. (PsycInfo Database Record (c) 2024 APA, all rights reserved).