Cognitive control (e.g., interference control) appears to be susceptible to time-on-task effects, i.e., there are fluctuations in the level of interference control over time. In two previous dual-task studies conducted in our lab, interference control assessed by the backward crosstalk effect (BCE) decreased with increasing time-on-task (Fischer et al., 2018; Jung et al., unpublished). Similar time-related changes have been observed in vigilance processes, known as the vigilance decrement (e.g., Mackworth, 1948). However, the relationship between reduced cognitive control and vigilance decrement remains unclear (Luna et al., 2022). Therefore, we aimed to assess time-on-task decrements of cognitive control, as assessed by changes in the BCE, simultaneously with a vigilance decrement, as assessed with an adapted ANTI-Vea task (Luna et al., 2021), in the same paradigm. In the dual task (60% of the trials), participants responded to the direction of two central arrows (i.e., the targets) appearing above (Task 1) and below (Task 2) the fixation point. In addition, executive vigilance (EV) trials (20%) required participants to detect a salient vertical displacement of the target in Task 1, while the remaining 20% of arousal vigilance (AV) trials involved stopping a millisecond counter as quickly as possible. Although the BCE in dual-task trials did not increase with time-on-task, we observed a Task 1-Task 2 performance trade-off over time, which was accompanied by a significant executive vigilance decrement, as is typically observed in the standard ANTI-Vea. The present outcomes motivate to further examine the relationship between cognitive control and vigilance loss across time-on-task.