Corticosteroid injections and foot orthoses are common interventions for plantar heel pain. Previous clinical trials have found that the effectiveness of these interventions differs over time, with corticosteroid injections being more effective in the short-term (i.e. 0-4 weeks) and foot orthoses more effective in the longer-term (i.e. 5-12 weeks). However, some of these trials have methodological weaknesses that could have caused confounding and bias, which may have led to over- or under-estimation of the effectiveness of these interventions. As a result, there is a need to compare the effectiveness of corticosteroid injections and foot orthoses in a robust clinical trial with an appropriate follow-up time.This article describes the protocol for a pragmatic, parallel-group assessor-blinded randomised trial (Steroid injection versus foot orthoses (SOOTHE) heel pain trial). One hundred participants with plantar heel pain will be randomly allocated (i.e. two groups of approximately 50) to receive either an ultrasound-guided corticosteroid injection or prefabricated foot orthoses. Outcome measures will be obtained at baseline, 4, 8 and 12 weeks, with two primary endpoints at 4 and 12 weeks to reflect the hypothesised temporal effects of each intervention. The primary outcome measure will be the foot pain domain of the Foot Health Status Questionnaire.Australian and New Zealand Clinical Trials Registry number ACTRN12615001266550.