Nano transition metal carbides (TMCs) have emerged as materials of great interest for different catalytic applications in fuel cells and also as catalysts for photo-treatment of organic effluents in industrial waste water. For both the catalytic phenomenon, the charge transfer pathways between the TMC and the surrounding carbon are of significant importance. In present work, well characterized nano powders of Tantalum Carbide (TaC) have been used as a model system to understand the effect and relative importance of powder parameters such as phase purity, particle size and amount of graphitic carbon (g-C) present (in the powder sample) in determining the performance for Hydrogen Evolution Reaction (HER) and photodegradation of Methylene Blue (MB) dye. For both the applications, TaC particle size and specific surface area (SSA) of the powder emerged as a key parameter. Larger SSA results in better performance even for powder with incomplete TaC phase formation. For same sized TaC, single phase powders give better performance. The SSA of the powders depends on the size of the carbide particles and the g-C present in the powders. The nature of synergistic interface between TaC and g-C emerges as an important parameter controlling the catalytic activity. This synergistic interface ensures that not only does the presence of g-C results in higher SSA but also, higher electron mobility by efficient charge transfer. The study of TaC powders with variable g-C content brought to fore the difference in the reaction pathways of the two catalytic systems in spite of the common requirement of charge transfer from TaC to g-C. As a consequence of the synergistic interface, dye adsorption properties of the g-C are modified by the presence of TaC and can be tailored. XPS, PL and UV data has been used to propose a possible degradation mechanism for the photo-oxidation of MB dye under visible irradiation.