Employee performance is commonly investigated as a static, one-time snapshot of prior employee behaviors. For the studies that do acknowledge that performance fluctuates over time, the timeframe decision is disconnected from theoretical underpinnings. To make this connection clearer, we draw on entrainment theory and investigate trajectories in motivation and performance across the 5-day workweek. We hypothesize that both motivational control (i.e., staying on course and sustaining effort in pursuit of goals through the redirection of attention) and performance have a declining trajectory across the workweek. Drawing on self-determination theory, we also hypothesize that trait-based mindfulness (i.e., nonjudgmental present moment attention and awareness) negatively relates to the downward trajectory in performance across the workweek via its effect on the trajectory of motivational control. Finally, we take a trait activation theory perspective, hypothesizing that mindfulness is relevant as an indirect influence on performance trajectories through motivational control trajectories only when job demands are high. We test our model using 151 full-time employees in a medical device company. We collected data from participants twice daily across the 5-day workweek. We then use these daily scores to create between-person (e.g., person-centric) trajectories to investigate the proposed relationships. The hypotheses are generally supported. There is a downward trajectory of both motivational control and performance across the workweek. Furthermore, job demands conditionally moderate the indirect effect of mindfulness on performance trajectories through motivational control trajectories. Theoretical and practical implications specific to dynamic motivation and performance, entrainment, and mindfulness literature are discussed. (PsycInfo Database Record (c) 2022 APA, all rights reserved).