Mori completed his Ph.D. titled "The Endomorphism Rings of Some Abelian Varieties" under Masayoshi Nagata at Kyoto University in 1978.

The classical approach used the concept of minimal models of algebraic surfaces.

He found that the concept of minimal models can be applied to three-folds as well if we allow some singularities on them.

The extension of Mori's results to dimensions higher than three is called the minimal model program and is an active area of research in algebraic geometry.

He has been elected president of the International Mathematical Union, becoming the first head of the group from East Asia.