Background: Fetal growth restriction (FGR) is associated with haemodynamic redistribution that preferentially reduces renal perfusion. Renal artery Doppler pulsatility index (PI) has been proposed as a non-invasive marker of this redistribution; however, clinically applicable diagnostic thresholds have not been established in Indian populations. Methods: This prospective comparative study enrolled 40 singleton pregnancies between 28 and 38 weeks of gestation: 20 with confirmed FGR (Group A) and 20 uncomplicated controls (Group B). Doppler PI and resistance index (RI) of bilateral fetal renal arteries, the middle cerebral artery, and the umbilical artery were measured using a 3.75-MHz curvilinear transducer. Receiver operating characteristic (ROC) curve analysis was performed to determine the optimal diagnostic PI threshold using Youden’s index. Results: Renal artery PI was significantly elevated in FGR for both the right kidney (2.57 ± 0.18 vs. 1.56 ± 0.16; p < 0.001) and left kidney (2.49 ± 0.18 vs. 1.59 ± 0.22; p < 0.001), with a large effect size (Cohen’s d ≥4.4). ROC analysis yielded an area under the curve (AUC) of 1.000 (95% CI: 0.999–1.000) for the right renal artery and 0.999 (95% CI: 0.990–1.000) for the left. A PI threshold of >2.10 for the right renal artery and >2.00 for the left offered sensitivity and specificity exceeding 97% for the diagnosis of FGR in this cohort. Renal artery RI did not differ significantly between groups. Fetal kidney dimensions correlated strongly with gestational age in both groups with no intergroup size difference. Conclusion: Fetal renal artery PI demonstrates excellent discriminatory performance for FGR, with near-perfect AUC values and diagnostically actionable thresholds (right renal PI >2.10; left renal PI >2.00). These thresholds warrant prospective validation in larger multicentre cohorts before integration into routine clinical surveillance protocols.