SMS reminders sent to personal mobiles are increasingly used by clinical services to promote patient engagement, including adherence to antiretroviral treatment (ART) for HIV. From August to September 2015, a 6-week, randomised SMS reminder for ART adherence intervention was implemented among 98 HIV-positive clients of Australian's largest HIV charitable organisation located in Sydney. This was followed by a mixed-method evaluation, comprising a self-completed online survey and a one-to-one interview. Of the 62 survey participants, all being men, the majority were gay (85.5%) and living long-term with HIV (median year of HIV diagnosis = 1998). While everyone was on ART, a substantial proportion (n = 27, 43.5%) had interrupted treatment in the past. At the end of the intervention, based on the standard SMAQ measure, 82% had consistently adhered to ART in the previous week. While there was no statistically significant intervention effect, perceiving less stigma were independently associated with better ART adherence (adjusted odds ratio = 0.37; 95% CI 0.16-0.89; P = .026). Of the 11 interviewees, despite limited add-on effects on individual ART adherence, the campaign was well-received as a unique community support service. This study underscores the essential role of empowerment through enhancing disease self-management, increasing social support and reducing stigma, particularly for long-term HIV survivors. SMS messaging, part of mHealth, delivered by community services could have broader impacts on reducing health and social inequity.