Background: Research on post-traumatic growth (PTG) and HIV is scarce and the relationship between PTG and stigma is controversial. Group psychotherapeutic interventions to facilitate PTG in clinical samples are effective but none exist to simultaneously decrease stigma in the HIV population. The main objective was to evaluate the effectiveness of an intervention in increasing PTG and decreasing stigma in HIV, as well as to explore relationships between the variables. Methods: Quasi-experimental design with a sample of 42 HIV-positive adults (M = 46.26, SD = 11.90). The experimental group (EG) was subjected to a 9-week group intervention. Instruments: CBI, PTGI-X, PSS-10, HIV stigma, emotional expression, HIV stress indicators, HIV literacy, and skills. Multiple linear regression analysis was performed to assess the relationship between the variables. Results: There was an increase in PTG and a significant decrease in stigma in all domains and subscales in the EG. Compared to the control group, stigma (t₍₄₂₎ = −3.040, p = 0.004) and negative self-image (W = −2.937, p = 0.003) were significant, showing the efficacy of the intervention. Discussion: The intervention demonstrated success in facilitating PTG, attesting that in order to increase PTG, personal strength, and spiritual change, it is necessary to reduce stigma and negative self-image. The research provides more information on group interventions for PTG in HIV, relationships between variables, and population-specific knowledge for professionals.