For the space of \((\sigma ,\tau )\)-derivations of the group algebra \( \mathbb {C} [G] \) of a discrete countable group G, the decomposition theorem for the space of \((\sigma ,\tau )\)-derivations, generalising the corresponding theorem on ordinary derivations on group algebras, is established in an algebraic context using groupoids and characters. Several corollaries and examples describing when all \((\sigma ,\tau )\)-derivations are inner are obtained. Considered in details are cases of \((\sigma , \tau )\)-nilpotent groups and \((\sigma , \tau )\)-FC groups.