IntroductionSocial media provide promising contemporary platforms for sharing public health information with a broad audience. Before implementation, testing social media campaigns that are intended to engage audiences and initiate behaviour change is necessary. This trial aims to investigate the effectiveness of a public health campaign to increase people’s confidence in becoming more active despite low back pain in comparison with no intervention.Methods and analysisThis is an online randomised controlled trial with two intervention groups and one control group in a 1:1:1 allocation. People over 18 years of age and fluent in English will be recruited via social media advertising. We developed a social media-based public health campaign to support recommendations for managing low back pain. The interventions are two videos. Participants in the control group will be asked questions about low back pain but will not view either video intervention. The primary outcome will be item 10 of the Pain Self-Efficacy Questionnaire, which asks participants to rate how confident they would feel to gradually become more active despite pain ranging from 0 (not at all confident) to 6 (completely confident). This outcome will be measured immediately in all participant groups. We will compare group mean of the three arms of the trial using univariate analyses of variance.Ethics and disseminationThis trial has been prospectively registered with the Australian New Zealand Clinical Trials Registry. We obtained ethical approval from our institutions Human Research Ethics Committee before data collection. We will publish the results in a peer-reviewed medical journal and on institution websites.Trial registration numberAustralian New Zealand Clinical Trials Registry (ACTRN12622000466741).