Background Homeless services expend considerable resources to provide for service users’ most basic needs, such as food and shelter, but their track record for ending homelessness is disappointing. An alternative model, Housing First, reversed the order of services so that homeless individuals are offered immediate access to independent housing, with wraparound supports but no treatment or abstinence requirements. Although the evidence base for Housing First’s effectiveness in ending homelessness is robust, less is known about its effectiveness in promoting recovery. Objective The objective of this research is to compare rehabilitation- and recovery-related outcomes of homeless services users who are engaged in either Housing First or traditional staircase services in eight European countries: France, Ireland, Italy, the Netherlands, Poland, Portugal, Spain, and Sweden. Methods A mixed methods, multi-site investigation of Housing First and traditional services will compare quantitative outcomes at two time points. Key rehabilitation outcomes include stable housing and psychiatric symptoms. Key growth outcomes include community integration and acquired capabilities. Semistructured interviews will be used to examine service users’ experiences of environmental constraints and affordances on acquired capabilities to identify features of homeless services that enhance service users’ capabilities sets. Multi-level modelling will be used to test for group differences—Housing First versus traditional services—on key outcome variables. Thematic analysis will be used to understand the ways in which service users make sense of internal and external affordances and constraints on capabilities. Results The study is registered with the European Commission (registration number: H2020-SC6-REVINEQUAL-2016/ GA726997). Two press releases, a research report to the funding body, two peer-reviewed articles, and an e-book chapter are planned for dissemination of the final results. The project was funded from September 2016 through September 2019. Expected results will be disseminated in 2019 and 2020. Conclusions We will use the findings from this research to formulate recommendations for European social policy on the configuration of homeless services and the scaling up and scaling out of Housing First programs. From our findings, we will draw conclusions about the setting features that promote individuals’ exits from homelessness, rehabilitation, and recovery. International Registered Report Identifier (IRRID) RR1-10.2196/14584