: The study evaluated the implementation of peer-based Mental First Aid (MFA) in a city organization. Its aim was to examine (1) the participants' user experiences of MFA, (2) the developmental needs of the MFA implementation process, and (3) whether and how the implementation of MFA changed the City's safety management. The data were from interviews, feedback from MFA testing and training, safety management documents, and a survey. MFA became established in the organization and there was a clear need for it. It was considered easy to use and had a low user threshold. It added value to traditional occupational safety and health practices by improving the participants' own practical skills to systematically manage the human factors of safety. MFA implementation needs clear management structures and a systematic commitment and learning process.