Background Smoking continues to be a leading risk factor for several diseases globally. We hypothesised that an intervention delivered via text messages could help individuals who were looking to quit.Methods A two-arm, parallel-groups, randomised controlled trial was employed. Both groups received treatment as usual, with the intervention group also receiving a 12-week text messaging intervention. Participants were adult, weekly or more frequent smokers, recruited online and in primary health care centres. Research personnel were blinded, while participants were not. Primary outcomes were prolonged abstinence and point prevalence of abstinence, 3 and 6 months post-randomisation. All randomised participants were included in analyses.Results Between 18 September 2020 and 16 June 2022, we randomised 1012 participants (intervention: 505, control: 507). Outcome data was available for 67% (n = 682) of participants at 3 months and 64% (n = 643) at 6 months. At 3 months, the odds ratio (OR) of prolonged abstinence was 2.15 (95% compatibility interval [CoI] = 1.51; 3.06, probability of effect [POE] > 99.9%, p < 0.0001), and for point prevalence of abstinence, it was 1.70 (95% CoI = 1.18; 2.44, POE = 99.8%, p = 0.0034) in favour of the text messaging intervention. At 6 months, the OR of prolonged abstinence was 2.38 (95% CoI = 1.62; 3.57, POE > 99.9%, p = < 0.0001), and for point prevalence, it was 1.49 (95% CoI = 1.03; 2.14, POE = 98.3%, p = 0.0349) in favour of the text messaging intervention. Analyses with imputed data were not markedly different.Conclusions Amongst general population help-seekers-who on average had smoked for 25 years-access to a 12-week text messaging intervention produced higher rates of self-reported smoking abstinence in comparison to treatment as usual only. The intervention could be part of the societal response to the burden which smoking causes; however, findings are limited by risk of bias due to attrition, self-reported outcomes, and lack of blinding.