In his years at the company, Ballmer became acquainted with a number of avant-garde contemporaries, including Hannes Meyer.

[2] In 1931, Ballmer joined the faculty of the Allgemeine Gewerbeschule Basel, where he taught photography and design.

[2] In the mid 1940s, Ballmer and his contemporary, Max Bill, pioneered a new style of graphic design characterized by the use of photography, sans serif typefaces, and logical arrangement of elements.

The work produced by the two designers in this period proved foundational to the later emergence of the International Typographic Style.

He is the father of Theo Ballmer II, who is famous for having created in 1971 the very recognizable logotype of Ouest-France, which is the most read francophone newspaper in the world, ahead of French national newspapers Le Figaro and Le Monde.