Proteinuria is a critical biomarker of kidney damage and a powerful predictor of progressive renal dysfunction. Valsartan, an angiotensin II receptor blocker (ARB), has emerged as a cornerstone therapy for proteinuria reduction across diverse renal pathologies. This comprehensive review synthesizes evidence from 187 studies examining valsartan’s efficacy, mechanisms of action, and clinical applications. The evidence demonstrates that valsartan consistently reduces proteinuria by 30–60% across various patient populations through multiple complementary mechanisms, including hemodynamic modulation, podocyte protection, anti-inflammatory effects, and oxidative stress reduction. Dose-dependent effects are observed, with higher doses (160–320 mg/day) providing enhanced renoprotection. The drug exhibits a favorable safety profile, although monitoring for hyperkalemia and renal function changes is essential. Valsartan shows particular efficacy in diabetic nephropathy (50% reduction), hypertensive nephropathy (48% reduction), and chronic kidney disease (45% reduction). This review establishes valsartan as a first-line therapeutic agent for proteinuric kidney diseases and identifies future research directions in personalized medicine and combination therapies.