Background and objectives: Delirium is a prevalent disorder that is associated with morbidity and mortality in hospitalized older adults. Recent evidence highlights sarcopenia, defined by low muscle mass, as a prognostic factor of importance. This study aims to investigate the association between sarcopenia, assessed by L3-level computed tomography (CT) and clinical outcomes, particularly mortality, in inpatients with delirium managed by a liaison psychiatry team (LPT). Methods: This single-center, retrospective observational study included 57 consecutive patients diagnosed with delirium and referred to the LPT at a tertiary care hospital between 2021 and 2023. Patients with available abdominal CT scans were included. Sarcopenia was defined based on the presence of low muscle mass observed at the L3 level on CT imaging, following established diagnostic criteria. The analysis included demographic data, clinical history, laboratory parameters, and treatment-related variables. Cox proportional hazards models and Kaplan–Meier survival curves were utilized to evaluate the association between sarcopenia and mortality during follow-up. Results: Of the 57 patients included, 52.6% (n = 30) were sarcopenic. Sarcopenia was associated with lower albumin levels (p = 0.038) and higher mortality rates (56.7% vs. 33.3%). Kaplan–Meier analysis showed reduced survival in sarcopenic patients (p = 0.038). Cox regression identified sarcopenia as an independent predictor of mortality (HR = 2.95; 95% CI: 1.03–8.46; p = 0.04), alongside the Charlson comorbidity index. Conclusions: Sarcopenia represents a robust and independent predictor of mortality in patients with delirium. Early nutritional assessment and targeted interventions addressing sarcopenia hold the potential to improve clinical outcomes. Further prospective studies with larger sample sizes are needed to validate these findings.