Generalised anxiety disorder (GAD) is a highly prevalent, chronic and impairing disorder. The aim of this study was to qualitatively describe the transformation in emotional processing across 16 sessions of a successful emotion-focused therapy (EFT) treatment for GAD. A theoretical framework derived from the EFT model of in-session emotional transformation proposed by Pascual-Leone and Greenberg was used as the basis for qualitative analysis. Additionally, the Classification of Affective Meaning States, the Client-Expressed Arousal Scale-III and the Client Emotional Productivity Scale-Revised were utilised by observer–raters to classify moment-by-moment shifts in client affective-meaning states, emotional arousal and emotional productivity. Results supported the emotion transformation model. The client presented in a state of poorly differentiated but highly aroused distress provoked by identifiable interpersonal and intrapersonal triggers. Emotional and behavioural avoidance provoked by fear of pain was evident. Accessing core pain and responding to attendant needs with compassion and protective anger was shown to facilitate the higher order emotional processing states of grief, relief and agency. Implications are proposed, including that addressing core emotional vulnerability may be a critical intervention in the successful treatment of GAD.