Understanding the roles and structures of social work practice in primary health care (PHC) is needed to strengthen the integration of social workers in team-based PHC. The main objective of this descriptive qualitative study was to understand social workers’ practice in the context of PHC in Ontario, Canada. We conducted focus groups with social workers embedded in PHC. Focus groups were recorded and transcribed verbatim. Thematic analysis guided an inductive analysis of the data. A total of N = 57 social workers participated in ten focus groups. We identified four themes in the data: (1) patient complexity in PHC, (2) multiple roles of social workers in PHC, (3) accessing social work services in PHC, and (4) recruitment and retention difficulties. Participants described variations in how patients accessed and engaged with social workers, and the multiple roles that social workers play in PHC. Social workers provide essential services in PHC that enhance the comprehensiveness and continuity of patient care. Greater attention is needed, however, on the structures that guide social work practice PHC—such as referrals, session caps, and pay equity—to ensure that social work is optimally contributing to the comprehensiveness of patient care in PHC.