Background: Discussing advance care planning (ACP) with care partners may be a steppingstone to the completion of advance directives (ADs) for persons with cognitive impairment (PwCIs). Objectives: To examine whether PwCI-reported occurrence of and PwCI-care partner agreement about ACP discussions are associated with completion of ADs. Design and Subjects: We conducted a secondary, cross-sectional analysis of data from 1672 PwCI-care partner dyads in the BLINDED study. PwCIs were Medicare beneficiaries in the US, aged >65 years, and diagnosed with mild cognitive impairment or dementia. Care partners were identified by PwCIs as being most involved in their health care. Measurements: PwCIs' completion of ADs was determined by 1 or more affirmative responses to dichotomous indicators for formalizing a living will, medical directive, or durable power of attorney for health care. Discussion occurrence was based on PwCI reports and agreement between PwCI and care partner reports of prior conversations about PwCIs' ACP preferences between PwCIs and care partners. Results: In logistic regression models adjusted for PwCI and care partner characteristics, PwCIs who had (vs. had not) discussed ACP were 10% more likely to complete ADs. PwCIs from dyads agreeing (vs. disagreeing) a discussion occurred were 7% more likely to complete ADs. PwCIs from care dyads in agreement (vs. disagreement) about non-discussion were 11% less likely to formalize ADs. Conclusions: Discussing ACP with care partners plays a direct, positive role in completing ADs among PwCIs. Health care providers who approach ACP as a dyadic, communicative decision-making process from the outset may facilitate PwCIs' uptake of ADs.