(1) Background: In 2011, new chronic disease guidelines were introduced across Mongolia. No formal advice was provided regarding role delineation. This study aimed to analyse the roles that different primary care providers adopted, and the variations in these, in the implementation of the guidelines in urban Mongolia; (2) Methods: Ten group interviews with nurses and ten individual interviews each with practice doctors and practice directors were conducted. Data was analysed using a thematic approach based on the identified themes relevant to role delineation; (3) Results: There was some variability and flexibility in role delineation. Factors involving teamwork, task rotation and practice flexibility facilitated well the guideline implementation. However, factors including expectations and decision making, nursing shortage, and training gaps adversely influenced in the roles and responsibilities. Some role confusion and dissatisfaction was identified, often associated with a lack of training or staff turnover; (4) Conclusions: Findings suggest that adequate ongoing training is required to maximize the range of roles particular provider types, especially primary care nurses, are competent to perform. Ensuring that role delineation is specified in guidelines could remove confusion and enhance implementation of such guidelines.