Grace Marion Waterhouse (23 July 1906 – 9 May 1996) was a British mycologist who worked for the International Mycological Institute in Kew for 20 years.

After graduation, she worked in the Botany Department of Royal Holloway College for 12 years.

Waterhouse was a student and collaborator of mycologist Elizabeth Marianne Blackwell (1889-1973); through her she became interested in the Phytophthora.

While at the International Mycological Institute, Waterhouse replaced Geoffrey Clough Ainsworth as the assistant editor of the Review of Applied Mycology, a journal dedicated to abstracting world literature on plant diseases.

She was also given the responsibility of identifying samples of plant pathogens belonging to the phycomycetes, which included Phytophthora.

She therefore wrote and published seminal keys to the genera Phythophthora, Sclerospora, Pythium, and Entomophthora.