Background: New-onset atrial fibrillation (NOAF) is a prevalent arrhythmia in critically ill cases. Serious mortality and morbidity are associated with it. The objective of this study was to assess the predictive value of the C-reactive protein (CRP)/albumin ratio (CAR) in critically ill patients admitted to the intensive care unit (ICU) regarding the occurrence of NOAF. Results: The participants in this observational research comprised 360 critically ill cases who were divided into two categories according to the onset of AF. Albumin and CRP levels in the serum were determined. CRP level divided by albumin level yielded the CAR ratio. NOAF predictors were identified utilizing multiple logistic regression analysis (MLRA).  NOAF was found in 18 (5%) of the patients. The CAR was greater in cases with NOAF than in cases without NOAF (p < 0.001). The CAR was an independent predictor of NOAF according to MLRA (95% confidence interval (CI): 1.219-1.836; odds ratio (OR) = 1.496; p < 0.001). CAR exhibited a significantly larger area under the receiver operating characteristic (ROC) curves (AUC) in AF prediction compared to CRP (0.878 vs. 0.869; p < 0.001). The CAR cut-off point for AF prediction was 3.1. Additionally, a statistically significant predictor of ICU mortality was identified in CAR (95% CI: 0.848-0.929; AUC: 0.889; p < 0.001). Conclusion: Patients who are critically ill with a high CAR at the time of admission have an increased risk of developing NOAF and worse clinical outcomes during hospitalization.