The Self-Determination Theory has been applied to explain behaviour in numerous contexts and cultures. In the exercise context, causality orientations (autonomy, control, impersonal) are important to describe individual differences in initiation and maintenance of health behaviour. The assessment of exercise causality orientations can be a key element to improve predictions of motivated health and exercise behaviour. Nevertheless, a scale to measure exercise causality orientations has not been established in German yet. Thus, it was the aim of the present work to translate the Exercise Causality Orientations Scale to German and to test it throughout three studies. The German G-ECOS questionnaire was cross-validated via confirmatory factor analyses in two separate samples. Both Study 1 (n = 306, 72.60% female, age M = 26.00, SD = 5.66; CFI = .96) and Study 2 (n = 320, 70.94% female, age M = 29.00, SD = 3.54; CFI = .95) indicated a good model fits. In a further Study 3 (n = 548, 62.50% female, age M = 30.17, SD = 11.91), the relations between exercise causality orientations and other SDT related constructs were examined. The correlations indicated positive associations between autonomy causality orientation and intrinsic regulation, intrinsic exercise participation goals, and exercise basic needs satisfaction. Overall, the assessment of exercise causality orientations can be useful in analysing and potentially predicting motivated exercise behaviour.