OBJECTIVES: Intrusive mental imagery is associated with anxiety in bipolar disorder (BD) and presents a novel treatment target. Imagery-based treatments show promise in targeting anxiety and improving mood instability. This qualitative study explored experiences of receiving up to 12 sessions of a brief structured psychological intervention: Image-Based Emotion Regulation (IBER), which targets maladaptive mental imagery in the context of BD with an aim to modify the emotional impact of these images. DESIGN: A qualitative study embedded within the Image Based Emotion Regulation (IBER) feasibility randomised controlled trial. METHODS: Semi-structured interviews were conducted with 12 participants in the treatment arm of the trial who received IBER + treatment as usual. Data were analysed using thematic analysis. RESULTS: Despite some initial scepticism about imagery-focused treatment, all participants expressed broadly positive accounts of treatment experiences. High levels of engagement with imagery modification techniques, beneficial use of techniques post treatment and improvements in anxiety management and agency were described by some. Three sub-groups were identified: those who reported a powerful transformative impact of treatment; those who embedded some new techniques into their daily lives, and those who felt they had techniques to use when needed. No participants reported overall negative experiences of the IBER treatment. CONCLUSIONS: Findings from this study highlight the value for treatment recipients of modifying the underlying meanings associated with maladaptive imagery, and the personalised skills development to manage anxiety within bipolar disorders. Findings can inform treatment refinements and further trial-based evaluations.