Europe requires significant transmission grid expansions to foster the integration of electricity markets, enhance security of supply and integrate renewable energies. However, next to lengthy authorization processes, transmission system operators (TSOs) in Europe are currently facing extreme public opposition in their transmission line projects leading to significant project delays. These delays imply significant additional costs for TSOs as well as society as a whole and put the transformation of the European energy system at risk. Existing scientific literature currently lacks comprehensive studies that have tried to identify generalizable success factors to overcome public opposition in transmission line projects. The goal of work at hand was to close this research gap. Potential success factors were collected through extensive literature review and interviews throughout Europe with respective stakeholders such as citizen action groups, NGOs or energy experts. Experiences from analogue large infrastructure projects like wind parks, carbon capture and storage facilities, hydro dams, nuclear waste repositories, etc. were also used to form hypotheses. The findings were transformed into a structural equation model and tested through a questionnaire answered by almost all European TSOs. Results revealed that people’s trust in the TSO is of utmost importance for less public opposition. It can be regarded as the critical success factor per se. TSOs can create trust through stakeholder participation, sufficient communication, proper organizational readiness and liaison with stakeholders. Furthermore, appropriate technical planning can help to reduce public opposition in transmission line projects. In total 18 concrete and actionable success factors were identified for TSO management to facilitate the establishment of these aforementioned aspects. They will help European TSOs to reduce public opposition and thus accelerate the implementation of new transmission lines. Interestingly, economic benefits for people did not turn out to be a Significant success factor in reducing their opposition against new transmission lines.