Fleet management based on connectivity is now evolving from simple location tracking towards becoming a cyber-physical mobility capability in which vehicles, roadside infrastructure, cloud platforms and operational teams constantly share data. This article looks at how Internet of Things technologies can help to achieve smart and sustainable fleet management in Saudi Arabia, with a focus on real-time visibility, predictive maintenance, route and energy optimisation, safety, interoperability, cybersecurity and environmental performance. A structured review of 30 peer-reviewed studies verified by DOI was carried out between 2020 and 2025. The evidence was organised using thematic synthesis rather than statistical aggregation since the body of literature includes a wide variety of fleet types, communication technologies, optimisation models and evaluation scenarios. The synthesis indicates that efficient fleet platforms rely on five interacting layers: reliable vehicle sensing, low-latency connectivity, edge-cloud data processing, decision intelligence, and governance that leads to measurable sustainability outcomes. The greatest operational benefits occur when these layers function as a closed loop so that telemetry data can be turned into actions such as changing routes, scheduling maintenance, giving driver feedback and making decisions about charging. Yet having good technical connectivity by itself does not ensure sustainable mobility; the benefits depend on the quality of the data, cybersecurity, interoperability, the electrification of the fleet, the readiness of the infrastructure and co-ordination at an institutional level. For Saudi Arabia, the literature recommends a step-by-step architecture that combines current telematics with 5G and vehicle-to-everything services, scalable edge-cloud analytics, common data models and performance governance. The review also suggests an implementation framework tailored to Saudi conditions and a number of indicators relating to operational performance, the environment, safety and digital resilience which are appropriate for fleet operators and mobility authorities.