In Saudi Arabia, the decarbonisation of urban bus transport is a critical component of the country's goal to achieve net zero emissions by 2060. With a specific focus on reducing GHG emissions from transportation, particularly urban buses that currently account for 22% of emissions, the country is exploring innovative vehicle technologies like hydrogen fuel cell vehicles (FCVs) and battery electric vehicles (BEVs). These technologies offer emission-free solutions during operation but require thorough life-cycle analysis considering factors like energy sources, production efficiency, and operational energy efficiency. The article discusses the production methods of hydrogen, categorizing them into green, blue, and grey hydrogen based on the feedstock and production processes. Saudi Arabia, with its significant natural gas reserves, currently finds grey and blue hydrogen more accessible and feasible than green hydrogen. The study also highlights the research gap in analyzing proton-exchange membrane (PEM) fuel cell buses (FCBs) and battery electric buses (BEBs) in the context of urban buses. To address these gaps, a comprehensive life-cycle analysis was conducted focusing on a potential bus fleet in Makkah, Saudi Arabia. Different scenarios for 2022 and 2030 were explored, considering the challenges of achieving renewable electricity for BEBs and transitioning to green hydrogen for FCBs. The study presents practical decarbonization strategies involving blue and grey hydrogen for FCBs and grid-connected BEBs as transitional solutions. By analyzing key environmental impact indicators and introducing a globally applicable life-cycle analysis model for bus systems, the study aims to provide insights into sustainable urban bus transport in Saudi Arabia and other non-OECD countries. The research emphasizes the importance of understanding the complete life cycle of vehicle technologies and infrastructure to make informed decisions towards decarbonization.