People with chronic inflammatory arthritis (IA) (rheumatoid arthritis, axial spondyloarthritis, and psoriatic arthritis), often have a reduced work ability. Up to 40% lose their job in the first years after diagnosis. Consequently, they are at high risk of losing their jobs and being permanently excluded from the labour market. Therefore, a new context-specific vocational rehabilitation (VR) for people with IA was developed, based on the Medical Research Council's framework for complex interventions. The 6-months VR is called WORK-ON and consists of three parts: 1) a coordinating occupational therapist who performs an initial assessment and goalsetting process and supports cooperation between relevant partners and navigation between sectors, 2) Four group sessions with peers and if needed, 3) Individual sessions with a social worker, nurse, or physiotherapist. The objective of the WORK-ON trial is to test the overall efficacy on work ability compared to a control group who receives usual care and pamphlets for their employer and colleagues. Based on the experiences from a feasibility study, WORK-ON will be conducted as a randomised controlled trial. Patients with IA, aged 18 years or older, experiencing job insecurity will be randomised to one of two groups: the WORK-ON VR group or usual care (control group). The primary outcome; work ability measured is measured by Work Ability Index single item, at baseline, 6, 12, 18 and 30 months after baseline. Secondary outcomes are absenteeism, presenteeism, overall work impairment, activity impairment, job loss, quality of life, mental well-being, fatigue, sleep, physical activity, occupational balance and pain. Secondary outcomes are measured at baseline, 6 and 12 months after baseline. In addition, work ability, working hours per week and job loss are measured at 18 and 30 months after baseline.