Background: In Catalonia a high percentage of the population remains inactive. General practices are an ideal setting to advise on physical activity (PA). However, there is a lack of evidence regarding practices, barriers and predictors of such promotion in the Catalan primary health-care system. This study set out to establish descriptive baseline data for PA promotion in Catalan general practices, and to explore the experiences of doctors/nurses in promoting PA in their day-to-day professional lives. Methods: A mixed-method approach was adopted. A survey was conducted with 245 physicians/nurses (58% response rate). Subsequently, focus groups (n = 5) and semi-structured interviews (n = 7) were conducted with 18 physicians and 15 nurses. After coding for important themes, the final interpretation was confirmed by contributors. Results: Eighty-eight percent of physicians/nurses promoted PA at least infrequently. However, work conditions were perceived as unfavourable, with the main barriers being lack of (i) time, (ii) training and (iii) protocols. Qualitative data showed that PA promotion was opportunistic, focused on selected patients, used generalized messages and was highly dependent on personal interests. Regular promotion was encouraged by direct experiences of the benefits of regular exercising, knowing patients well, being supported by medical colleagues and creating links with other community institutions. PA promotion was especially hindered by seeing PA promotion as a secondary task, and patients ignoring recommendations. Conclusion: PA promotion in Catalonia remains to be integrated into practice consultations. Therefore, strategies should be developed within public health. Using a mixed-method approach provided a broader range of evidence than most studies, which rely on quantitative methods.