Stefan Ydefeldt was first educated at the University of Music in Gothenburg, after which he was engaged as a pianist at the Gothenburg Opera. He continued his piano studies in Stockholm with Professor Gunnar Hallhagen and obtained a piano teacher's degree and a church musician's degree.

In his professional life, Ydefeldt has combined teaching work with concert activities, where in addition to a solo performance, he has worked with a large number of constellations with chamber music and romance repertoire. He is currently active as an organist in Täby parish. During his piano studies with Gunnar Hallhagen, his interest in the history of piano technique and the movements of piano playing developed. The studies inspired him to many years of research, which has received attention both nationally and internationally. This research forms the basis of his book The simple circular motion – a study in philosophies of motion at piano playing distributed by Gehrmans Musikförlag.