BACKGROUND: Patients with non-severe ANCA-associated vasculitis (AAV) are often prescribed immunosuppressive medications that are associated with severe side effects and a reduced quality of life. There is an unmet need for safer effective treatments for these patients. Hydroxychloroquine is being explored due to its effect in similar autoimmune conditions such as systemic lupus erythematosus. METHODS: Double-blind, placebo-controlled multicentre trial recruiting 76 patients across 20 sites. Participants will be randomised 1:1 to hydroxychloroquine or placebo in addition to standard of care immunosuppressive therapies over the course of 52 weeks. A phase II selection design will be used to determine hdroxychloroquine's efficacy, using prednisolone dosage and Birmingham Vasculitis Activity Score as a measure of disease activity. Secondary outcomes will explore other elements of AAV progression, including disease flares and time to remission. DISCUSSION: This trial aims to explore Hydroxychloroquine as a treatment for patients with AAV. If effective, the need for immunosuppressive treatments such as prednisolone could be reduced. Hydroxychloroquine is safer, cheaper and has fewer adverse effects than conventional immunosuppressive treatments. This could improve patient outcomes while saving money for the NHS. TRIAL REGISTRATION: ISRCTN: ISRCTN79334891. Registered 07 June 2021. EudraCT: 2018-001268-40. Registered 13 September 2019. CLINICALTRIALS: gov: NCT04316494. Registered 20 March 2020.