Research on intervention development has expanded over the past decade. However, much of the extant literature on complex intervention development is confined to healthcare and public health broadly or intervention science specifically with scant attention to the process within other fields known for their extensive provision of social interventions such as social work or community-based services. This paper aims to advance understanding of the complex intervention development process within social work using an example from the Swedish municipal social services. We use the Guidance for Reporting Intervention Development Studies (GUIDED) to describe the development and content of My Choice-My Way! an intervention to support youth transitioning from out-of-home care. Youth in out-of-home care is an extremely vulnerable group and one of social welfare services’ core user populations. Coproduction processes were used to develop a theory-, evidence-, and implementation-based approach to intervention development. Implications for future development within social work are discussed.