Iontronics are rapidly emerging technologies with strong potential in sensing and energy harvesting. By leveraging ion transport, electrochemical interactions, and electron-ion coupling, iontronic systems have driven advancements in intelligent sensing and sustainable energy harvesting. This review explores the efficiency and suitability of iontronics for next-generation sensing and energy harvesting applications, emphasizing their advantages over conventional electronic approaches. We provide a comprehensive summary of the latest technological developments in iontronic neuromorphic sensors and energy harvesters, particularly focusing on working mechanisms of iontronic devices driven by ion dynamics, which facilitate the development of intelligent and energy-efficient sensing and harvesting devices. Understanding these fundamental mechanisms enables the optimization of iontronic materials and device structures for enhanced functionality and broader applications. Finally, this review discusses the current challenges and future directions in advanced iontronic sensing and energy harvesting technologies, providing insights into how continued research and development can further enhance their capabilities and technological integration in practical applications.