The present paper deals with the study of new generalized fractional integral operator involving $$K_4$$ K4 -function due to Sharma. Mellin and Laplace transforms of this new operator are investigated. The bounded-ness and composition properties of the proposed operator are also established. Further, derived results are applied to solve fractional differential equation involving $$K_4$$ K4 -function associated with Hilfer derivatives. The $$K_4$$ K4 -function is further extension of M-series and the importance of desired results lies in the fact that many known results are readily follows as special cases of our finding. $$K_4$$ K4 and M-series have recently found essential application in solving problems of science, engineering and technology. Some special cases of the established results are given in form of corollaries.