Background <p>Post-neurosurgical bacterial meningitis (PNBM) is a severe complication after neurosurgery, and early diagnosis remains challenging. This study aimed to develop and validate a diagnostic nomogram for identifying PNBM in postoperative neurosurgical patients.</p> Methods <p>Postoperative neurosurgical patients with clinically suspected meningitis admitted to the neurosurgical intensive care unit of Nanfang Hospital between January 15, 2020 and January 15, 2025 were retrospectively analyzed. A diagnostic nomogram was developed using multivariable logistic regression and internally validated using bootstrap resampling. An independent cohort (<i>N</i> = 63) enrolled between January 16, 2025 and December 16, 2025 was used for external validation. Diagnostic performance was assessed using the area under the receiver operating characteristic curve (AUC), calibration plots, and decision curve analysis.</p> Results <p>Cerebrospinal fluid (CSF) white blood cell count, CSF lactate concentration, and CSF glucose concentration were identified as independent diagnostic factors and incorporated into the nomogram. The diagnostic nomogram demonstrated excellent discrimination with an AUC of 0.933 in the development cohort and 0.908 in the validation cohort, outperforming individual CSF parameters (<i>P</i> &lt; 0.001, DeLong’s test). Calibration curves showed good agreement between predicted and observed probabilities. Decision curve analysis indicated favorable clinical utility.</p> Conclusions <p>This diagnostic nomogram provides an effective and convenient tool for early identification of post-neurosurgical bacterial meningitis.</p>