His life and achievements were honoured in a Solid State Ionics symposium commemorating his 100th birthday in 2001, where he was described as the father of solid-state chemistry.

He also researched problems of solid-state chemistry, especially the role of defects of ionic crystals on thermodynamic properties, electrical conductivity and diffusion.

[4][5] In 1936 he published a crucial paper "On the mechanism of the formation of ionic crystals of higher order (double salts, spinels, silicates)", a concept of counter-diffusion of cations, which contributed to the understanding of all diffusion controlled, solid-state reactions.

[5]: 94 For these works and his subsequent research on local equilibrium, his oxidation rate theory, and the concept of counter diffusion of cations, Wagner is considered by some as the "father of solid state chemistry.

Wagner was invited to the United States to become a scientific advisor at Fort Bliss, Texas, with other German scientists as part of Operation Paperclip.

He then returned to Germany to take up the position of Director of the Max Planck Institute of Physical Chemistry at Göttingen, which was vacant due to the untimely death of Karl Friedrich Bonhoeffer.

[10] Wagner officially retired in 1966 but from 1967 to 1977 was a Scientific Member of the Max Planck Institute in Göttingen, continuing to contribute to publications.

[11] Many modern inventions based on solid-state technology and semiconductor fabrication, used in devices such as solar energy conversion have been developed with the aid of Wagner's theories.