The physic metallurgy process is a complex phenomenon that co-occurs, for example, the grain nucleation, diffusion, dendritic and grain structure growth, fluid flow behavior, the development of gas bubbles, porosity, cracking, etc. Physic metallurgy investigation in material science and manufacturing processes is mainly based on “ex-situ” observations by advanced instruments for EBSD, SEM, EPMA, EDS, etc. However, they are constrained by less information, and the ability to explore the “real-time” phenomena is challenging. Therefore, developing and using “in-situ” and “real-time” observation using X-ray synchrotrons to improve understanding of underlying phenomena is indispensable. This can support the rapid development of new materials and novel manufacturing processes. This paper reviews the development and capability of “in-situ” X-ray techniques as an invaluable tool for material science and advanced manufacturing. The main focusing of this review is on using welding and additive manufacturing processes as they are the key and emerging topics to attend the investigation of a number of groups in the world.