Kawashima attended Tokyo University of the Arts where he completed post-graduate work. In 1992 he won the Akiyoshidai International Composition Prize, and the Kranichsteiner Musikpreis at the Darmstadt International Summer Course in 1996. He was awarded the Akutagawa Award for Music Composition in 1996, the Nakajima Kenzo Music Prize in 2009 and the Toshi Ichiyanagi Contemporary Prize in 2017. As well as working as program advisor for Izumi Sinfonietta Osaka, he is involved in many contemporary music events and commentary projects; he appeared on the popular variety TV program as a commentator for a contemporary music special.
He produces two regular concert series, "Works of Motoharu Kawashima" as his portrait concert from 2017, and "Motoharu Kawashima plays" as his recital from 2020. He also undertakes conducting (member of "Ensemble Kochi") and other variable performances, mainly of his own works and contemporary pieces.
He is a Vice-president of The Japan Federation of Composers Inc., an Associate Professor at Kunitachi College of Music, and lecturer at Tokyo College of Music and Shobi University.