Purpose There are currently many diabetes apps available, but there is limited evidence demonstrating clinical impact. The purpose of this study is to evaluate the impact of a diabetes mobile app with in-app coaching by a certified diabetes educator on glycemic control for individuals with type 2 diabetes. Methods A 12 week-long single-arm intent-to-treat trial evaluated the impact of a diabetes mobile app and coaching program (One Drop | Mobile With One Drop | Experts), which facilitated tracking of self-care and included an in-app diabetes education program, on A1C for individuals with type 2 diabetes and an A1C ≥7.5% (58 mmol/mol). An online study platform (Achievement Studies, Evidation Health Inc, San Mateo, CA) was used to screen, consent, and enroll participants; collect study data; and track participants' progress throughout the study. Baseline and study end A1C measurements as well as questionnaire data from participants were collected. Results Participants (n = 146) were 52 ± 9 years old, 71% female, 25% black or Hispanic, diagnosed with diabetes for 11 ± 7 years, and with a mean baseline A1C of 9.87% ± 2.0 (84 mmol/mol). In adjusted repeated measures models, mean A1C improved by -0.86% among study completers (n = 127), -0.96% among active users of the app and coaching program (n = 93), and -1.32% among active users with a baseline A1C ≥9.0% (75 mmol/mol) (n = 53). Conclusions This program was associated with a clinically meaningful and significant reduction in A1C and can potentially increase access to effective diabetes self-management education and support for individuals with diabetes.