The pre-processing and value-added production of leafy agricultural commodities—particularly green tea and medicinal herbs—constitute a pivotal component of Vietnam’s agricultural value chain and rural household economy. Nevertheless, ensuring consistent product quality remains a persistent challenge, largely due to dependence on manual roasting practices or rudimentary equipment lacking precise thermal regulation. This study presents the research, design, and simulation of a compact roasting system for leafy agricultural products, employing a rotary drum mechanism with a processing capacity of 3–5 kg per batch. The central objective is to optimize both the mechanical configuration and the control architecture in order to maximally preserve color, aroma, and thermolabile bioactive compounds. The proposed system incorporates a horizontally aligned cylindrical drum fabricated from food-grade stainless steel (Inox 304), ensuring compliance with food safety standards and superior resistance to high-temperature chemical corrosion. Within the drum, a set of four symmetrically configured agitator blades facilitates homogeneous mixing and multi-point heat transfer. A notable contribution of this work lies in the utilization of SolidWorks software to construct a detailed 3D model and perform kinematic simulations, enabling the prediction of thermal energy distribution within the drum prior to physical prototyping. The system is further integrated with a PLC-based intelligent control unit and a variable frequency drive (VFD), allowing precise regulation of drying temperature within an acceptable tolerance range, thereby enhancing moisture removal efficiency and ensuring operational stability. Experimental validation demonstrates that the system operates reliably, producing outputs with a final moisture content below 13.5%, in compliance with QCVN 01-54:2011/BNNPTNT standards. Additionally, the system reduces labor intensity by approximately 40% and achieves significant energy savings compared to conventional direct-heating methods. This research provides an advanced mechanical solution that contributes to the modernization of post-harvest processing technologies for smallholder farmers, in alignment with sustainable agricultural development strategies.