IntroductionAchilles tendinopathy (AT) is a common and disabling musculoskeletal condition. First-line management involving Achilles tendon loading exercise with, or without, other modalities may not resolve the problem in up to 44% of cases. Many people receive injections. Yet there are no injection treatments with demonstrated long-term efficacy. The aim of the trial is to examine the 12-month efficacy of high-volume injection (HVI) with corticosteroid and HVI without corticosteroid versus sham injection among individuals with AT.Methods and analysisThe trial is a three-arm, parallel group, double-blind, superiority randomised controlled trial that will assess the efficacy of HVI with and without corticosteroid versus sham up to 12 months. We will block-randomise 192 participants to one of the three groups with a 1:1:1 ratio, and both participants and outcome assessors will be blinded to treatment allocation. All participants will receive an identical evidence-based education and exercise intervention. The primary outcome measure will be the Victorian Institute of Sport Assessment – Achilles (VISA-A) at 12 months post-randomisation, a validated, reliable and disease-specific measure of pain and function. Choice of secondary outcomes was informed by core outcome domains for tendinopathy. Data will be analysed using the intention-to-treat principle.Ethics and disseminationEthics approval was obtained via the Monash University Human Ethics Committee (no: 13138). The study is expected to be completed in 2024 and disseminated via peer review publication and conference presentations.Trial registration numberAustralia and New Zealand Clinical trials registry (ACTRN12619001455156)