After graduation from the Gymnasium in Duisburg, Nohl studied jurisprudence at the universities in Bonn, Heidelberg, and Berlin, where he received instruction in music from Siegfried Dehn and Friedrich Kiel.

In 1860 he wrote his thesis on Mozart and earned the rank of privatdozent for "History and Aesthetic of Musical Art."

In 1865 he was awarded by King Ludwig II the title of Professor of Music at the University of Munich for his compilation of Mozart's letters.

In that year he discovered through the "industrial teacher" Babeth Bredl in Munich the now-lost autograph of Beethoven's Bagatelle Für Elise.

His main legacy is as a Beethoven scholar, and a portion of his writings are housed at the state archive in Iserlohn.