Gudmund Sundby (18 January 1878 – 16 February 1973) was a Norwegian hydroelectric engineer and university professor.

He was a son of Halvor Gudmundsen Sundby and Gina Jakobsdatter.

He was a student at Kristiania Technical School (today a part of Oslo University College) and took the mechanical engineering exam in 1898, after which he was employed by Kværner.

Sundby was a member of the Royal Norwegian Society of Sciences and Letters from 1928.

A portrait of Sundby, painted by Jean Heiberg, is located at the Norwegian University of Science and Technology.