BACKGROUND: The implementation of diabetes prevention for women with previous gestational diabetes (GDM) has been stymied by many barriers that are located within routine general practice (GP). We aimed to unpack the GP factors and understand the mechanisms that explain why a diabetes prevention intervention for this population succeeds or fails. METHODS: We performed a mixed-methods study with a Normalization Process Theory framework that included clinical audits, semistructured interviews, and focus groups within mixed urban and rural primary care practices in Victoria, Australia. Staff of primary care practices and external support staff who provide services to women with previous GDM participated in a 12-month quality improvement collaborative intervention. We compared diabetes screening and prevention activity planning with the strategies and factors identified through a process evaluation of full-, moderate-, and low-active participating practices. RESULTS: The intervention doubled screening rates (26%-61%) and 1-in-10 women received a diabetes prevention planning consultation. Critical improvement factors were: mothers being seen as participants in the quality improvement work; staff collectively building care strategies; staff taking a long-term care of a community perspective rather than episodic service delivery; and feedback processes being provided and acted on across the practice. The observable factors from the external perspective were: leadership by identified practice staff, reminder systems in action and practice staff driving the process collectively. CONCLUSIONS: Successful engagement in diabetes prevention for women with previous GDM requires proactive building of the critical improvement factors and audit feedback into routine GP.