Although interventions can increase advance care planning (ACP) engagement, it remains unclear which interventions to choose in primary care settings. This study compares a passive intervention (mailed materials) to an interactive intervention (group visits) on participant ACP engagement and experiences. We used mixed methods to examine ACP engagement at baseline and six months following two ACP interventions. Eligible patients were randomized to receive mailed materials or participate in two ACP group visits. We administered the 4-item ACP Engagement survey (n = 110) and conducted interviews (n = 23). We compared mean scores and percent change in ACP engagement, analyzed interviews with directed content analysis to understand participants' ACP experiences, and integrated the findings based on mailed materials or group visits intervention. All participants demonstrated increased ACP engagement scores. At six months, group visit participants reported higher percent change in mean overall score compared with mailed materials participants (+8% vs +3%, P < .0001). Group visits participants reported that being prompted to think about end-of-life preferences, gaining knowledge about ACP, and understanding the value of completing ACP documentation influenced their ACP readiness. While both interventions encouraged patients to start considering and refining their end-of-life preferences, group visits made patients feel more knowledgeable about ACP, highlighted the importance of completing ACP documentation early, and sparked further ACP discussions with others. While primary care patients may benefit from mailed ACP materials, patients reported increased readiness after ACP group visits. Group visits emphasized the value of upstream preparation, ongoing conversations, and increased knowledge about ACP.