BACKGROUND: Non-communicable diseases (NCDs) contribute greatly to morbidity and mortality in low-income and middle-income countries (LMICs). Community health workers (CHWs) may improve disease control and medication adherence among patients with NCDs in LMICs, but data are lacking. We assessed the impact of a CHW-led intervention on disease control and adherence among patients with diabetes and/or hypertension in Chiapas, Mexico. METHODS: We conducted a prospective observational study among adult patients with diabetes and/or hypertension, in the context of a stepped-wedge roll-out of a CHW-led intervention. We measured self-reported adherence to medications, blood pressure and haemoglobin A1c at baseline and every 3 months, timed just prior to expansion of the intervention to a new community. We conducted individual-level mixed effects analyses of study data, adjusting for time and clustering by patient and community. FINDINGS: We analysed 108 patients. The CHW-led intervention was associated with a twofold increase in the odds of disease control (OR 2.04, 95% CI 1.15 to 3.62). It was also associated with optimal adherence assessed by 30-day recall (OR 1.86; 95% CI 1.15 to 3.02) and a positive self-assessment of adherence behaviour (OR 2.29; 95% CI 1.26 to 4.15), but not by 5-day recall. INTERPRETATION: A CHW-led adherence intervention was associated with disease control and adherence among adults with diabetes and/or hypertension. This study supports a role of CHWs in supplementing comprehensive primary care for patients with NCDs in LMICs. TRIAL REGISTRATION NUMBER: NCT02549495.