INTRODUCTION: Plasma biomarkers of Alzheimer's Disease and Related Dementias (ADRD) pathology may help clarify associations between modifiable risk factors (MRFs) and cognitive and functional impairment. METHODS: Cross-sectional data from 1002 adults (mean age 72.0 ± 6.7) enrolled in the Bio-Hermes-001 study were analysed. First, block regression models assessed the added predictive value of MRFs and ADRD plasma biomarkers on cognitive (Mini-Mental State Examination, [MMSE]) and functional outcomes (Functional Activities Questionnaire, [FAQ]), beyond MRFs alone. Second, latent path analysis (LPA) examined potential pathways linking MRFs, ADRD biomarkers, and cognition and functional outcomes. RESULTS: ADRD biomarkers significantly improved prediction models for MMSE (ΔR2 = 0.11) and FAQ scores (ΔR2 = 0.11). Indirect effects consistent with mediation were observed for depression (B = -0.05), BMI (B = 0.02), and tobacco use (B = 0.14) in relation to cognitive and functional outcomes. DISCUSSION: ADRD biomarkers are relevant to pathways linking MRFs with cognitive and functional outcomes and have potential for risk stratification and prevention research. Longitudinal studies are needed to determine temporal relationships and clarify potential causal mechanisms.