BACKGROUND: Muscle weakness and fatigability, the prominent symptoms of autoimmune myasthenia gravis (MG), impact negatively on daily function and quality of life (QoL). It is currently unclear as to what extent symptoms limit activity and whether physical activity (PA) behaviours are associated with reduced QoL. OBJECTIVES: This study aimed to describe habitual PA patterns and explore relationships between PA metrics, clinical MG characteristics, and health-related QoL (HRQoL). METHODS: PA data from a trunk tri-axial accelerometer worn for seven days, was collected from females with generalized, stable MG and compared to control subjects. MG-specific evaluations, the six-minute walk test and knee extension strength were assessed in individuals with MG (IwMG). Mann-Whitney tests were used to study between-group differences. Spearman rank correlation coefficient was performed to explore relationships between variables. RESULTS: Thirty-three IwMG (mean (SD) age 45 (11) years) and 66 control subjects were included. IwMG perform less vigorous-intensity PA than control subjects (p = 0.001), spend more time sedentary (p = 0.02) and engage in less and shorter durations of moderate-vigorous-intensity PA (MVPA). For IwMG, habitual PA correlated positively with 6 min walking distance (rho = 0.387, p = 0.029) and negatively with body mass index (rho = -0.407, p = 0.019). We did not find any association between PA or sedentary behaviour and; HRQoL, symptom severity nor lower limb strength. CONCLUSIONS: Individuals with stable MG perform less PA, at lower intensities, and are more inactive than controls individuals. Further research is warranted to understand factors influencing PA patterns in MG and whether interventions could be successful in increasing PA quantity and intensity in IwMG.