Policy research can reveal gaps and opportunities to enhance policy impact and implementation. In this study, we use a theoretically informed qualitative approach to investigate the implementation of two policies to promote breastfeeding in Vietnam. We conducted semi-structured interviews with national and local policy stakeholders (n = 26) in 2017. Interviews were audio-recorded, transcribed verbatim and then translated to English by certified translators. Transcript data were analysed using an integrated conceptual framework of policy implementation. Respondents identified several positive outcomes resulting from implementation of an extended maternity leave policy (Labour Code No. 10/2012/QH13) and further restrictions on marketing of breast milk substitutes (Decree No. 100/2014/ND-CP). Decree No. 100, in particular, was said to have reduced advertising of breast milk substitutes in mass media outlets and healthcare settings. Key implementation actors were national-level bureaucratic actors, local organizations and international partners. Findings reveal the importance of policy precedence and a broader set of policies to promote the rights of women and children to support implementation. Other facilitators were involvement from national-level implementing agencies and healthcare personnel and strength of government relationships and coordination with non-governmental and international organizations. Implementation challenges included insufficient funding, limited training to report violations, a cumbersome reporting process and pervasive misinformation about breast milk and breast milk substitutes. Limited reach for women employed in the informal labour sector and in rural communities was said to be a compatibility issue for the extended maternity leave policy in addition to the lack of impact on non-parental guardians and caretakers. Recommendations to improve policy implementation include designating a role for international organizations in supporting implementation, expanding maternity protections for all working women, building local-level policy knowledge to support enforcement, simplifying Decree No. 100 violation reporting processes and continuing to invest in interventions to facilitate a supportive policy environment in Vietnam.