Haller started with the profession of carpenter. From 1948 he worked as an employee with various Swiss architects. A year later, he became self-employed. At first he was still working with his father. He was also employed by the Construction Research Institute (Konrad Wachsmann) in California as a freelancer. From 1977 Haller taught as a professor architecture in Karlsruhe. There he also directed the Institute for Building Design. The Institute for Industrial Construction was under its management from 1990 onwards.
Together with Paul Schärer, Fritz developed steel tube furniture for USM Haller (named after him). In principle, the design provided for a modular system, in which the designers oriented themselves. These furniture were always expandable, adaptable and changeable, so they could adapt to any given and changing situation. This made them extremely flexible. Conversion is also possible. It is also impressive that extensions do not only apply to newer models. It is possible to connect cabinets from the 1960s with today's new elements. For this achievement Haller was awarded the Swiss Prize for Sustainability.