He is renowned for his contributions to the field of structural engineering, such as Mohr's circle, and for his study of stress.

Starting in 1855, his early working life was spent in railroad engineering for the Hanover and Oldenburg state railways, designing some famous bridges and making some of the earliest uses of steel trusses.

Even during his early railway years, Mohr had developed an interest in the theories of mechanics and the strength of materials.

In addition to a lone textbook, Mohr published many research papers on the theory of structures and strength of materials.

Mohr was an enthusiast for graphical tools and developed the method, for visually representing stress in three dimensions, previously proposed by Carl Culmann.