The present study aimed: (1) to test the associations of overall physical fitness and subjective well-being with fibromyalgia severity and (2) to determine whether the combination of overall physical fitness and subjective well-being is associated with fibromyalgia severity among adult women patients. This cross-sectional study included 424 participants from Andalusia, southern Spain. Overall physical fitness and the components of subjective well-being (positive affect, negative affect and cognitive well-being), and fibromyalgia severity were assessed using the Functional Senior Physical Fitness Test Battery, the Positive and Negative Affect Schedule, the Satisfaction With Life Scale, and the Fibromyalgia Impact Questionnaire, respectively. Overall physical fitness (beta = -.23), positive affect (beta = -.18), negative affect (beta = .26), and cognitive well-being (beta = -.18) were all associated with fibromyalgia severity. The patients with the highest overall physical fitness and increased subjective well-being reported similar to 15 % lower fibromyalgia severity than those with the lowest fitness and poorest subjective well-being (Cohen’s d > 1.0). Our results suggest that higher levels of overall physical fitness and subjective well-being are independently associated with lower fibromyalgia severity. Moreover, patients with higher overall physical fitness and increased subjective well-being (high positive affect, low negative affect, or high cognitive well-being) reported lower fibromyalgia severity than those with low levels of overall physical fitness and subjective well-being.