Mental fatigue has previously been reported to impair subsequent endurance performance. However, uncertainty regarding the veracity of this effect remains. Moreover, the effect of heightened perception of fatigue on common perceptual (i.e. effort) and affective modulators of endurance performance also requires further study. The present study therefore examined two hypotheses: (1) that mental fatigue impairs muscular endurance performance and (2) that the perception of fatigue evoked through sustained cognitive exertion is related to the degree of effort and affect reported during a subsequent endurance task. Eighteen participants performed an exhaustive, submaximal (20% maximal voluntary contraction, MVC) isometric contraction of the right knee extensor muscles, following both a protracted high and low cognitively demanding task. The high cognitive demand task (HIGH) evoked greater perceptions of fatigue and poorer cognitive performance. However, both endurance performance and perceptions of effort and affect recorded during the endurance task were not different between cognitive tasks. Significant correlations were found between perceptions of fatigue and both perceived effort and affective responses. In conclusion, mental fatigue did not impair muscular endurance performance nor influence perceived effort and affective responses. The observed relationships offer some support to the idea that fatigue perception reflects an overarching controller of performance regulatory processes. However, the absence of direct performance effects may indicate that fatigue perception following cognitive vs. physical exertion may emerge through distinct processes.