Purpose Sarcopenia is an increasingly recognised marker of physiological vulnerability in surgical patients, yet its impact on outcomes after kidney transplantation remains unclear. This study evaluated the relationship between psoas muscle index (PMI)–defined sarcopenia and post-transplant outcomes, with a focus on patient survival. Methodology We performed a retrospective cohort study of 331 adult kidney transplant recipients transplanted between 2019 and 2025 at a tertiary centre. Pre-transplant CT-derived PMI at the L3 vertebral level was available for approximately 260 patients and indexed to height. Sarcopenia was defined using established sex-specific thresholds (≤6.6 cm²/m² for males and ≤4.8 cm²/m² for females). PMI was analysed as both categorical and continuous variables. The primary outcome was 12-month mortality. Secondary outcomes included graft-related outcomes, length of stay, and post-operative complications. Multivariable logistic regression adjusted for age, body mass index, frailty score, and dialysis duration. Results Sarcopenia was prevalent and associated with greater frailty and longer dialysis duration. PMI-defined sarcopenia was associated with approximately a two-fold increase in unadjusted 12-month mortality. On adjusted analysis, lower PMI as a continuous measure remained independently associated with mortality, along with dialysis duration. No significant associations were observed between sarcopenia and graft-related outcomes. Urinary and wound complications were the most common post-operative events among sarcopenic recipients. Conclusion PMI-defined sarcopenia identifies kidney transplant recipients at increased risk of early post-transplant mortality but does not predict graft outcomes. Routine assessment of muscle mass using pre-transplant imaging may improve peri-operative risk stratification and inform targeted optimisation strategies.