Aims Volumetric Modulated Arc Therapy with Simultaneous Integrated Boost (VMAT-SIB) enables highly conformal dose delivery with superior sparing of organs at risk (OAR) compared to conventional radiotherapy techniques. Although international studies have demonstrated favorable efficacy and toxicity outcomes, data from resource-limited South Asian settings remain scarce. This study reports the initial institutional experience with VMAT-SIB for locally advanced head and neck squamous cell carcinoma (HNSCC) in Bangladesh. Methodology This retrospective analysis included 30 consecutive patients with stage III–IVB HNSCC treated with definitive VMAT-SIB between January and December 2025 at a tertiary oncology center in Bangladesh. Dose prescriptions were as follows: high-risk PTV—70 Gy, intermediate-risk PTV—60 Gy, and elective PTV—56 Gy, all delivered in 33 fractions. Concurrent weekly cisplatin was administered when clinically appropriate. Primary endpoints included acute toxicity (graded per RTOG criteria), early locoregional control (LRC), and dosimetric parameters. Results The median patient age was 61 years, with 80% being male. The oropharynx was the most common primary tumor site. Median follow-up was 12 months. All patients achieved ≥95% PTV coverage. The mean conformity index was 1.052, mean homogeneity index was 0.124 and all OAR dose constraints were met as per RTOG guidelines. The most frequent acute toxicity was oral mucositis; grade 3 mucositis occurred in 21% of patients. At 6 months, the locoregional control rate was 78.6%. Conclusion VMAT-SIB provided excellent target coverage, satisfactory OAR sparing, and acceptable acute toxicity in this Bangladeshi cohort with locally advanced HNSCC. Early locoregional control outcomes are comparable with international series, underscoring the feasibility and effectiveness of VMAT-SIB in resource-constrained environments. Extended follow-up is warranted to assess long-term disease control and late toxicity profiles.