Objective: Seriously ill adults with multiple chronic conditions (MCC) who receive palliative care may benefit from improved symptom burden, health care utilization and cost, caregiver stress, and quality of life. To guide research involving serious illness and MCC, palliative care can be integrated into a conceptual model to develop future research studies to improve care strategies and outcomes in this population. Methods: The adapted conceptual model was developed based on a thorough review of the literature, in which current evidence and conceptual models related to serious illness, MCC, and palliative care were appraised. Factors contributing to patients’ needs, services received, and service-related variables were identified. Relevant patient outcomes and evidence gaps are also highlighted. Results: Fifty-eight articles were synthesized to inform the development of an adapted conceptual model including serious illness, MCC, and palliative care. Concepts were organized into 4 main conceptual groups, including Factors Affecting Needs (sociodemographic and social determinants of health), Factors Affecting Services Received (health system; research, evidence base, dissemination, and health policy; community resources), Service-Related Variables (patient visits, service mix, quality of care, patient information, experience), and Outcomes (symptom burden, quality of life, function, advance care planning, goal-concordant care, utilization, cost, death, site of death, satisfaction). Discussion: The adapted conceptual model integrates palliative care with serious illness and multiple chronic conditions. The model is intended to guide the development of research studies involving seriously ill adults with MCC and aid researchers in addressing relevant evidence gaps.