This study presents a process planning system, which directly generates manufacturing code from CAD models for robotic wire and arc additive manufacturing (WAAM). A variety of modules are developed for this system with special considerations on slicing and path planning. Multi-direction slicing methodology is developed to allow the WAAM system to deposit material along multiple directions and eliminate the need for supporting structure. MAT-based path planning method is proposed for void-free deposition of layers with any complex geometry. The proposed automatic process planning system is an important tool for the development of mature WAAM technology.