The transportation sector plays a vital role in managing urban solid waste (USW) and significantly contributes to greenhouse gas (GHG) emissions. This study assesses the carbon footprint of USW collection in Fornos de Algodres, a municipality of Portugal, by comparing diesel trucks and electric trucks under various electricity supply scenarios. The analysis utilizes real-world operational data, including fuel and electricity consumption, emission factors, and vehicle efficiency. The results indicate that electrifying the waste collection fleet can reduce CO₂ emissions by between 29.3% and 87.1%, depending on the electricity supplier and the energy consumption of the trucks. Currently, the municipality sources electricity from Suppliers A and B, with Supplier A resulting in lower emissions (4259–8845 kgCO₂eq per year) compared to Supplier B (9,363–19,445 kgCO₂eq per year). A cleaner option, Supplier C, has the potential to further reduce emissions (3549–7371 kgCO₂eq per year) due to its more favourable energy mix. The findings emphasize that electrification alone is insufficient to fully maximize environmental benefits—the carbon footprint of electric trucks largely depends on energy efficiency and the electricity mix used. To optimize GHG reductions, municipalities should combine fleet electrification with cleaner electricity sources. This study offers valuable insights for policymakers and waste management companies, supporting goals related to sustainable urban mobility and climate action. Future research should focus on the economic feasibility, operational costs, and integration of renewable energy sources to further enhance sustainability.