Though he wrote his PhD thesis in Germanic literature, entitled Vers oder Prosa im hohen Drama des achtzehnten Jahrhunderts (1914), and taught languages at school, where Erich Kästner was one of his pupils, he devoted his life to art research and publishing.

After the First World War, he wrote many entries for the Thieme-Becker and articles for the periodical Der Cicerone [de].

He was also a friend of Karl Schmidt-Rottluff, Otto Dix, Paul Klee, Wassily Kandinsky and Oskar Schlemmer.

Grohmann published over 500 essays on more than 150 artists, among them Edvard Munch, Ernst Barlach, Henri Matisse, Pablo Picasso and Joan Miró, and about 1,300 newspaper articles, not to mention his many catalogue forewords.

[1] Furthermore, he was engaged in curating important exhibitions and "played a significant role in drawing international attention to the avant-garde".