PurposeThe purpose of this paper is to demonstrate how action research-based interventions can effect change in a complex and challenging professional service environment (Lewis and Brown, 2012). This paper presents a successful way to do this. First, by eliciting factors for change driven by deregulation in the United Kingdom’s (UK) legal service sector (Falconer, 2005). Second, by designing and implementing context-sensitive change in a selected legal service firm.Design/methodology/approachThis research adopts a participatory action research methodology involving the use of systems thinking (namely the PrOH modelling methodology) to design suitable interventions and catalyse change.FindingsThis study has generated new knowledge on three fronts–to the legal service operations, to methodology and to the intellectual framework used for abductive reasoning (Checkland and Poulter, 2006). Lessons are transferable to wider professional service operations research. Findings indicate, despite traditional challenges of delivering typical professional services, there is potential for rationalising processes and service delivery commodification, mainly in the low volume, high variety legal service typology (Silvestro et al., 1992).Research limitations/implicationsThis research uses data from an in-depth study of a single organisation.Practical implicationsThis research helped legal service professionals to improve overall efficiency and effectiveness and create new management tools.Social implicationsThis research could help improve legal service operations and make them more accessible.Originality/valueThis research applies a novel, systems thinking based methodology for the first time in a complex professional service operations environment leading to three-fold contributions in the areas of practice, theory and methodology. The paper uses a change management framework (the Change Kaleidoscope), a soft systems methodology (PrOH modelling) and applies these to legal services.