Abstract Background Long duration of untreated psychosis (DUP) is associated with poor outcomes and low quality of life at first contact with mental health services. However, long DUP is common. In order to inform initiatives to reduce DUP, we investigated service users' and carers' experiences of the onset of psychosis and help-seeking in two multicultural, inner London boroughs and the roles of participants' social networks in their pathways to care. Method In-depth interviews were conducted with service users and carers from an early intervention service in North London, purposively sampled to achieve diversity in sociodemographic characteristics and DUP and to include service users in contact with community organisations during illness onset. Interviews covered respondents' understanding of and reaction to the onset of psychosis, their help-seeking attempts and the reactions of social networks and health services. Thematic analysis of interview transcripts was conducted. Results Multiple barriers to prompt treatment included not attributing problems to psychosis, worries about the stigma of mental illness and service contact, not knowing where to get help and unhelpful service responses. Help was often not sought until crisis point, despite considerable prior distress. The person experiencing symptoms was often the last to recognise them as mental illness. In an urban UK setting, where involved, workers in non-health community organisations were frequently willing to assist help-seeking but often lacked skills, time or knowledge to do so. Conclusion Even modest periods of untreated psychosis cause distress and disruption to individuals and their families. Early intervention services should prioritise early detection. Initiatives aimed at reducing DUP may succeed not by promoting swift service response alone, but also by targeting delays in initial help-seeking. Our study suggests that strategies for doing this may include addressing the stigma associated with psychosis and community education regarding symptoms and services, targeting not only young people developing illness but also a range of people in their networks, including staff in educational and community organisations. Initiatives to enhance the effective involvement of staff in community organisations working with young people in promoting help-seeking merit research.