This study compares completion and recovery rates between protocol-based cognitive behavioural therapy (CBT), offered as a first-line therapy for common mental health problems as per national guidelines, and relational therapies (RTs), scarcely provided in the English Improving Access to Psychological Therapies (IAPT) programme. This is a non-randomized, naturalistic study in a treatment-seeking community sample (n = 708). RTs consist of brief psychodynamic and relational integrative therapy. Completion rates relied on clinicians’ coding and recovery rates were calculated based on the Patient Health Questionnaires-9 and the Generalized Anxiety Disorder-7. Doubly robust regression analysis was used to control both the treatment allocation and outcome variables for pretreatment differences between the intervention groups. Significantly more RT clients completed treatment compared with CBT clients. No significant differences in recovery rates between CBT and RTs were found using traditional null hypothesis significance tests; the groups were found to be equivalent using equivalence tests. Only when the analysis was repeated in treatment completers did CBT clients achieve around one-quarter higher recovery rates. Both CBT and RTs appeared to be equally effective and showed recovery and completion rates equivalent to or above the national average. These findings demonstrate the advantages of therapies other than CBT. Future research is needed to replicate the equivalence between these two treatments and to explore specific patient characteristics that make one treatment more suitable and acceptable than the other.