Purpose: There is considerable variation in the physical and psychological presentations of people with whiplash-associated disorder (WAD). Optimal treatment continues to be a challenge. This research evaluated the efficacy of a community-located, theory-based intervention designed to promote physically active behaviour in people with persistent WAD, and thereby improve perceptions of pain interference and confidence completing activities in the presence of neck pain. Materials and methods: A multiple-baseline, single-case experimental design was used to evaluate the 16-week intervention across six participants. Results: Weighted Tau-U showed significantly increased accelerometer-measured physical activity in three participants with large effect sizes (>0.5), with increased confidence in one participant (ES > 0.5), and reduced pain interference in another participant (ES > 0.7). Changes in other behaviours included clinically important improvements in quality of life for five participants and, in those participants with baseline symptom levels outside threshold levels, improvements in pain catastrophizing and pain self-efficacy. Conclusions: Participation in a theory-based intervention resulted in significant improvements in physical and psychological health for five of six participants. Providing this type of community-located physical activity promotion strategy, to individuals with persistent WAD, may help address physical impairments and psychological distress commonly experienced in WAD.