IMPORTANCE Despite lacking robust evidence of effectiveness, health care systems in developed countries are funding holistic community health worker (CHW) social prescribing programs that address social needs and health behaviors as adjuncts to clinical care. OBJECTIVE To determine whether a UK National Health Service (NHS) CHW social prescribing program was associated with improved hemoglobin A 1c (HbA 1c ) levels among patients with type 2 diabetes. DESIGN, SETTING, AND PARTICIPANTS This cohort study with difference-in-differences analysis was conducted among 8086 patients (4752 in the referral program, 3334 in the control group) in 24 NHS primary care practices in a city in North East England. Patients aged 40 to 74 years with a diagnosis of type 2 diabetes were observed for 8 years, from 2011 through 2019. The statistical analysis was conducted between