Objective: This study aimed to evaluate the effectiveness of a combination of Schema Therapy and ACT (Acceptance and Commitment Therapy) in reducing overcompensation coping strategies associated with early maladaptive schemas in patients diagnosed with histrionic personality disorder (HPD). Methods: A randomized quasi-experimental design with a comparison group was used, involving pre-test, post-test, and a two-month follow-up assessment. Participants were 30 HPD patients selected from three psychology centers in 2021–2022 in Tehran who met the inclusion criteria for HPD diagnosis based on clinical interviews and Millon Clinical Multiaxial Inventory-III (MCMI-III). Patients were randomly assigned to either the intervention or waitlist group. The intervention group received ten 90-minute sessions of combined therapy. MCMI-III and the Young Compensation Inventory (YCI) were used as research instruments. Multivariate analysis of covariance was used to control for pre-treatment differences between the intervention and waitlist groups and to assess the effect of the intervention on the outcome measures. Results: The intervention group had significantly lower MCMI-III Disclosure scores and lower YCI levels immediately post-treatment and at the two-month follow-up assessment compared to the waitlist control group. The effect sizes for these comparisons were large to very large, indicating a significant and clinically meaningful improvement in the intervention group. Conclusions: The findings suggest that combined Schema Therapy and ACT may be effective in reducing overcompensation coping strategies in HPD patients. The study's limitations included the absence of random sampling in the first stage of screening. Future research should aim to replicate these findings with larger samples and diverse populations.