Imdahl studied studio painting, art history, archaeology and German literature at the University of Münster.
For his paintings he won the Blevins Davis Prize, the most prestigious art contest of the postwar period in Germany,[2] in 1950.
In 1951 he completed his Ph.D. dissertation on the treatment of color in late Carolingian book illustration under Werner Hager.
He worked as an assistant professor at the University of Münster for some years and wrote his Habilitationsschrift on Ottonian Art in 1961.
Imdahl formulated a methodology he called "the Iconic," using an artwork's structure to determine its significance.