Early in Peter Keil's career his style was influenced by German expressionism. In the works from his early Berlin years, he mainly focused on people on the fringes of society and city scenes.
The 1960’s, and living in Paris briefly, brought a change to Keil’s work He departed from the realistic art he had been painting and introduced a more free spirited and loose style. After moving to London he continued to explored this new approach.
Keil's energetic, dynamic, and intense color and brush work have become hallmarks of his work.