He worked at the University of Tokyo from April in 1959 to May 1967 as a lecturer (1959-1962) and as an assistant professor (1962–1967).

Nagano moved to United States to pursue an academic career with the University of Notre Dame in 1967.

Tadashi Nagano co-authored 10 papers with Shoshichi Kobayashi in the interval 1966–1972, including A theorem on filtered Lie algebras and its applications, Bull.

[6] Tadashi Nagano served an editor-in-chief of Tokyo Journal of Mathematics for several years since 1990.

In 1994, Tadashi Nagano was presented with the Geometry Prize from Mathematical Society of Japan[7] for his research achievements over a large field of the differential geometry including a geometric construction of compact symmetric spaces; known as the (M+,M-)-theory (or Chen-Nagano theory) co-created with Bang-Yen Chen.