Background Multicomponent workplace-based interventions aimed at reducing sitting time among office workers are becoming increasingly popular. `Take a Stand!' was such an intervention, reducing sitting time by 71min after 1month and 48min after 3months. However, it is unclear how the implementation process of `Take a Stand!' affected these results. The present study explored how individual factors and organizational context influenced implementation and effect in `Take a Stand!'MethodsThis was a mixed-methods study, combining data from interviews, questionnaires and accelerometers. Directed content analysis was used for analysing interviews with participants, ambassadors and managers from the 10 intervention offices in the `Take a Stand!' study. Categories for analysis were taken from Framework for Evaluating Organizational-level Interventions. Interview data were combined with questionnaire and activity data, and multilevel analysis was undertaken to assess how changes in sitting time varied depending on the assessed factors. In addition, interview data were used to underpin results from the multilevel analysis.ResultsConcurrent institutional changes were found to be a barrier for the intervention by ambassadors, while participants and managers did not find it to be an issue. Management support was consistently highlighted as very important. Participants evaluated ambassadors as being generally adequately active but also, that the role had a greater potential.The motivational and social aspects of the intervention were considered important for the effect. This was supported by regression analyses, which showed that a strong desire to change sitting time habits, strong motivation towards the project, and a high sense of collective engagement were associated to less sitting time at 3months of about 30min/8h working day compared to participants with low scores. Influence from other participants (e.g. seeing others raise their tables) and the use of humour were continuously highlighted by participants as positive for implementation. Finally, the intervention was found to influence the social climate at the workplace positively.ConclusionIndividual motivation was related to the sitting time effect of `Take a Stand!', but the organizational culture was relevant both to the implementation and effect within the office community. The organizational culture included among others to ensure general participation, to uphold management and peer-support, and maintain a positive environment during the intervention period.Trial registrationClinicalTrials.gov, NCT01996176. Prospectively registered 21 November 2013.