ObjectivesDespite the established evidence base for mental health peer support work, widespread implementation remains a challenge. This study aimed to explore societal and organisational influences on the implementation of peer support work in low-income and high-income settings.DesignStudy sites conducted two focus groups in local languages at each site, using a topic guide based on a conceptual framework describing eight peer support worker (PSW) principles and five implementation issues. Transcripts were translated into English and an inductive thematic analysis was conducted to characterise implementation influences.SettingThe study took place in two tertiary and three secondary mental healthcare sites as part of the Using Peer Support in Developing Empowering Mental Health Services (UPSIDES) study, comprising three high-income sites (Hamburg and Ulm, Germany; Be’er Sheva, Israel) and two low-income sites (Dar es Salaam, Tanzania; Kampala, Uganda) chosen for diversity both in region and in experience of peer support work.Participants12 focus groups were conducted (including a total of 86 participants), across sites in Ulm (n=2), Hamburg (n=2), Dar es Salaam (n=2), Be’er Sheva (n=2) and Kampala (n=4). Three individual interviews were also done in Kampala. All participants met the inclusion criteria: aged over 18 years; actual or potential PSW or mental health clinician or hospital/community manager or regional/national policy-maker; and able to give informed consent.ResultsSix themes relating to implementation influences were identified: community and staff attitudes, resource availability, organisational culture, role definition, training and support and peer support network.ConclusionsThis is the first multicountry study to explore societal attitudes and organisational culture influences on the implementation of peer support. Addressing community-level discrimination and developing a recovery orientation in mental health systems can contribute to effective implementation of peer support work. The relationship between societal stigma about mental health and resource allocation decisions warrants future investigation.Trial registration numberISRCTN26008944.