The Mental Health Recovery Star (MHRS) is a therapeutic tool and outcome measure, used widely in the UK and internationally for clients and keyworkers in mental health services to jointly assess and work towards client-centred recovery goals. As such it has been recognised as potentially offering a means of building a positive working alliance between clients and workers. The alliance is increasingly being highlighted as a key common factor across therapeutic models that may underpin positive clinical outcomes. This study employed Grounded Theory Methods to explore the alliance within the context of using the MHRS in rehabilitation mental health services. Semi-structured interviews were carried out with ten clients and four workers across three services. The findings are presented in a theoretical model that explains the core category that emerged from this study – “being engaged in working together towards improved wellbeing”. Working with the MHRS was seen to inform three particular alliance processes: collaborative working; negotiating new or shared perspectives; and motivation towards improved wellbeing. The findings also highlighted challenges that can hinder these processes when using the MHRS, calling for improvements in practices of negotiation and better support for workers. Further clinical implications alongside avenues for future research are discussed.